Rozprawy doktorskie na temat „Mechanism of action”
Kliknij ten link, aby zobaczyć inne rodzaje publikacji na ten temat: Mechanism of action.
Utwórz poprawne odniesienie w stylach APA, MLA, Chicago, Harvard i wielu innych
Sprawdź 50 najlepszych rozpraw doktorskich naukowych na temat „Mechanism of action”.
Przycisk „Dodaj do bibliografii” jest dostępny obok każdej pracy w bibliografii. Użyj go – a my automatycznie utworzymy odniesienie bibliograficzne do wybranej pracy w stylu cytowania, którego potrzebujesz: APA, MLA, Harvard, Chicago, Vancouver itp.
Możesz również pobrać pełny tekst publikacji naukowej w formacie „.pdf” i przeczytać adnotację do pracy online, jeśli odpowiednie parametry są dostępne w metadanych.
Przeglądaj rozprawy doktorskie z różnych dziedzin i twórz odpowiednie bibliografie.
1
Tatarski, Miloš. "Molecular mechanism of dBigH1 action". Doctoral thesis, Universitat de Barcelona, 2018. http://hdl.handle.net/10803/663021.
Pełny tekst źródłaStreszczenie:
INTRODUCTION:
For decades it was known that many species contain embryo specific linker histone H1 variants that replace the somatic H1 during early embryogenesis. This is especially important because the early embryo shows typically zero to very little activity of transcription, and the first cleavages of the embryo depend exclusively on maternally deposited factors that are important for transcription and chromatin assembly. The first species shown to contain an embryo specific histone H1 was the sea urchin. Other species like the mouse, Xenopus or the zebrafish followed. Even in humans there are embryo specific H1 variants. Drosophila seemed to be an exception to this, until in 2013 the first linker histone H1 variant was discovered that was called dBigH1. Like other embryo H1 variants, dBigH1 is expressed in the early embryo and disappears when cellularization starts and it gets replaced by the somatic H1. Likewise, to its counterparts in other species, dBigH1 is responsible for the inhibition of transcription during the early stage of fly development.
OBJECTIVES:
In this thesis, we addressed the questions about the mechanism of inhibition of dBigH1 as well as the factors that are responsible for its deposition into chromatin.
RESULTS:
To answer the first question, we used an in vitro system for chromatin reconstitution based on an extract from early Drosophila embryos (DREX) that contains dBigH1 and all other factors needed for proper chromatin assembly. We then used the reconstituted chromatin in transcription experiments using HeLa nuclear extract that contains all factors needed for transcription.
We saw that transcription for chromatin reconstituted in DREX could be reduced when the extract was previously depleted from dBigH1 using specific antibodies against it. By adding back recombinant dBigH1 to the depleted extract we were able to restore the initial lever of transcription. This showed us that dBigH1 was the repressive factor, as it was already confirmed in vivo.
We then used a truncated construct of dBigH1 where we depleted the N-terminal domain of the protein. This was of particular interest as the N-terminal region of dBigH1 is the one that differs most form the somatic H1. It is much longer and more importantly very enriched with acidic residues, something that is very unique amongst all embryo specific H1 variants. We saw that when using the truncated construct, transcription was inhibited to a much lesser extent than with the full length dBigH1, proposing that the N-terminal domain is indeed responsible for the inhibition of transcription.
To answer the second question about the factors needed for dBigH1 deposition, we used Drosophila testis to study dBigH1 in vivo. dBigH1 shows a very similar expression pattern in testis as the chromatin remodeler ACF1. This is why we decided to investigate a possible interaction between those two proteins. Additionally, we knew that ACF1 uses NAP1 as a histone chaperone for H1 in some species, so we also asked if NAP1 could play a role in dBigH1 deposition as well.
Indeed, we saw that when using flies deficient for ACF1 we see much less dBigH1 in the testis tip where the germal stem cells (GSC) reside, suggesting that ACF1 plays an important role in dBigH1 deposition. In accordance, we see more dBigH1 in the GSCs when using flies overexpressing ACF1. At the same time, we can see that when depleting NAP1 from DREX, we see more dBigH1.
2
Attarzadeh, Yazdi Ghassem. "Molecular mechanism of glucocorticoid action". Thesis, University of Edinburgh, 2006. http://hdl.handle.net/1842/26161.
Pełny tekst źródłaStreszczenie:
The aim of this thesis project was to investigate the mechanisms by which glucocorticoid hormones regulate the activity of BK channels in human embryonic kidney 293 (HEK293) cells as the model system for glucocorticoids-action. It was shown that glucocorticoids act via endogenously expressed type II receptors in a concentration- and time-dependent manner in these cells. Dexamethasone (100 nM) had no significant effect on Dexras1 mRNA but significantly increased serum- and glucocorticoid-induced protein kinase 1 (SGK-1) mRNA. Biochemical analysis showed that SGK-1 protein is increased by dexamethasone in a Triton X-100 insoluble fraction. Further work was directed toward analysing the possible association of SGK-1 and protein phosphatases with two BK channel α-subunit variants: ZERO-BK and STREX-BK, the latter contains the 59 amino-acid splice insert encoded by the stress hormone induced exon (STREX). HEK293 cells stably expressing the respective channel subunits were analysed. Immunoprecipitations with antisera directed against the BK α-subunits showed that protein phosphatase 2A (PP2A) but not SGK-1 is constitutively associated with the STREX as well as the ZERO variant BK channel. Furthermore, the cytoplasmic C-terminal segment of the STREX-BK channel was necessary for cell-surface expression of the channel and the association of the channel with PP2A. Dexamethasone, failed to change the apparent amount of immunoreactive PP2A co-immunoprecipitating with the channel. In conclusion: SGK-1 but not Dexras1 is a protein rapidly induced by dexamethasone in HEK293 cells. PP2A but not SGK-1 is in complex with both ZERO and STREX-BK channels, and dexamethasone does not alter this association. The cytoplasmic tail of the BK channels is essential for PP2A interaction.
3
Conti, Lucio. "The molecular mechanism of TFL1 action". Thesis, University of East Anglia, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.423575.
Pełny tekst źródłaStreszczenie:
During Arabidopsis development the shoot apical meristem (SAM) generates lateral primordia which display stage-specific traits. In long days, wild-type Arabidopsis generates leaves in an initial vegetative phase (V). Upon integration of environmental and endogenous signals, the SAM enters the reproductive phase. First it makes an 11 phase, which consists of 2-3 leaves (cauline) subtending secondary shoots (coflorescences). Next it enters the 12 phase and produces flowers on its flanks. The TFL 1 gene is a key component of the phase change machinery as mutations in TFL 1 affect the timing of phase switching. Also ffl1 mutants enter a novel phase whereby the SAM, after 12, is converted into a terminal flower, a phase normally absent in wild type. The molecular mechanism of how TFL 1 protein acts is unclear. In animal systems, TFL 1-like proteins have been shown to be components of signal transduction pathways. To understand the mechanism underlying TFL 1 function I aimed to identify proteins interacting with TFL 1 by introducing into Arabidopsis a functional TAP tag version of TFL 1 under the control of the 35S promoter. I set up conditions which allowed me to isolate and visualize by total protein staining TAPtag TFL 1. However, no obvious proteins appeared to co-purify with TFL 1. To understand how TFL 1 is modified, and to follow TFL 1 protein expression throughout development and in cell fractions, I developed polyclonal antibodies against TFL 1. These antibodies recognized TFL 1 in vivo and were used to characterize TFL 1 biochemically. TFL 1 detection by immunoblots in conjunction with mass-spectrometry analysis showed that TFL 1 was not subjected to obvious modifications unlike animal homologues. Moreover, from cellular fractionation experiments TFL 1 was located in the cytosol. To reveal essential downstream functions required for TFL 1 signaling, I characterized a suppressor mutant, called sof1, of plants ectopically expressing TFL 1. I mapped sof1 within a confined region on the bottom of chromosome 3. Physiological analysis of sof1 led to a model of SOT1 action in controlling phase change. TFL 1 mRNA is found in a unique expression domain which comprises a group of cells in the centre of the SAM and yet TFL 1 affects the identity of lateral primordia. By using affinity purified anti-TFL 1 antibodies I showed that TFL 1 protein moves and is distributed throughout the SAM. This might account for the effect of TFL 1 on controlling overall shoot identity and raises important questions on the role of the TFL 1 protein outside its mRNA expression domain.
4
Beastall, J. C. "The mechanism of action of azone". Thesis, University of Nottingham, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380112.
Pełny tekst źródła
5
Williams, Daffydd Griffin. "Mechanism of action of penetration enhancers". Thesis, Cardiff University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320625.
Pełny tekst źródła
6
Taylor, Catherine. "A mechanism of action of strigolactone". Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709140.
Pełny tekst źródła
7
Taylor, M. R. G. "Mechanism of action of Rad51 paralogs". Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1458671/.
Pełny tekst źródłaStreszczenie:
Homologous recombination (HR) is an essential DNA break repair mechanism that remains incompletely understood. HR is a complex multistep process initiated by the loading of RAD-51 recombinase as filaments onto single stranded DNA (ssDNA). This structure directly invades an intact homologous duplex, which serves as a template for repair DNA synthesis. Numerous positive regulators of HR have been described, including the Rad51 paralogs, but the mechanism of action of Rad51 paralogs in promoting HR is unknown. In this study, I have characterized the mechanism of action of a novel Rad51 paralog complex, RFS-1/RIP-1, from C. elegans. RFS-1 is a Rad51 paralog required for RAD-51 focus formation at stalled replication forks, indicating an early positive regulatory role in HR. I demonstrate that RFS-1 interacts with a nematode-specific orphan protein, RIP-1. I identify a cryptic Walker B ATPase-like motif within RIP-1, which is functionally important in establishing the RFS-1/RIP-1 interaction interface. rip-1 and rfs-1 mutant animals phenocopy for essentially all phenotypes analysed. Together these data suggest RFS-1/RIP-1 functions as a constitutive complex. I show recombinant RFS-1/RIP-1 can be purified and specifically binds ssDNA but lacks measurable ATPase activity. RFS-1/RIP-1 also strongly stimulates strand invasion activity by RAD-51, consistent with a pro-recombinogenic function in vivo. I define for the first time the mechanism of action underlying the intrinsic ability of Rad51 paralogs to stimulate HR. Using a combination of biochemical and biophysical approaches, notably electrophoretic mobility shift assays, stopped-flow reaction kinetics and nuclease protection assays, I show RFS-1/RIP-1 dramatically alters the properties of RAD-51-ssDNA filaments such that RAD-51 is more stably associated with ssDNA yet the ssDNA is more sensitive to nuclease degradation. RFS-1/RIP-1 exerts these effects primarily downstream of filament formation, ruling out a major role in RAD-51 loading. I propose RFS-1/RIP-1 remodels RAD-51-ssDNA filaments to a conformation poised for pairing with the template duplex and strand invasion.
8
Phisit, Prapunwattana Yongyuth Yuthavong. "Mechanism of antimalarial action of tetracycline /". abstract, 1986. http://mulinet3.li.mahidol.ac.th/thesis/2529/29E-Phisit-P.pdf.
Pełny tekst źródła
9
Díaz, i. Cirac Anna. "Mechanism of action of cyclic antimicrobial peptides". Doctoral thesis, Universitat de Girona, 2011. http://hdl.handle.net/10803/38252.
Pełny tekst źródłaStreszczenie:
This PhD thesis is the result of the combination of experimental and computational techniques with the aim of understanding the mechanism of action of de novo cyclic decapeptides with high antimicrobial activity.
By experimental techniques the influence of the replacement of the phenylalanine for tryptophan residue in their antimicrobial activity was tested and the stability in human serum was also analyzed, in order to evaluate their potential therapeutic application as antitumor agents.
On the other hand, the interaction amongst the peptide BPC194 c(KKLKKFKKLQ), the best candidate from the whole library of cyclic peptides, and a model anionic membrane was simulated. The results showed a structure-function relationship derived from the stable conformation of the peptides involved in the membrane permeabilization. As a result, a rational design was performed being BPC490 the peptide with best antimicrobial activity compared with the best active peptide from the original library.Aquesta tesi doctoral resulta de la combinació d’estudis mitjançant tècniques experimentals i computacionals amb l’objectiu d’entendre el mecanisme d’acció de "de novo" decapèptids cíclics amb elevada activitat antimicrobiana. Experimentalment, es va avaluar la influència de la substitució dels residus de fenilalanina per triptòfan en la seva activitat antimicrobiana i també la seva estabilitat sèrum humà, per tal de valorar la seva possible aplicació terapèutica envers el càncer. Per altra banda, es va simular la interacció del pèptid BPC194 c(KKLKKFKKLQ), millor candidat de la biblioteca de pèptids cíclics, amb models aniònics de bicapa lipídica. Els resultats van posar en manifest una relació estructura-funció derivada de la conformació estable dels pèptids que participen directament en la permeabilització de la membrana. Es va procedir doncs al disseny racional de nous pèptids cíclics sent el pèptid BPC490 el que va presentar una millor activitat bacteriana en comparació amb el pèptid més actiu de la llibreria original.
10
Reißmann, Stefanie. "Mechanism of Action of Group II Chaperonins:". Diss., lmu, 2007. http://nbn-resolving.de/urn:nbn:de:bvb:19-73195.
Pełny tekst źródła
11
Hirschkorn, Martin C. "Dynamic Model of a Piano Action Mechanism". Thesis, University of Waterloo, 2004. http://hdl.handle.net/10012/877.
Pełny tekst źródłaStreszczenie:
While some attempts have been made to model the behaviour of the grand piano action (the mechanism that translates a key press into a hammer striking a string), most researchers have reduced the system to a simple model with little relation to the components of a real action. While such models are useful for certain applications, they are not appropriate as design tools for piano makers, since the model parameters have little physical meaning and must be calibrated from the behaviour of a real action. A new model for a piano action is proposed in this thesis. The model treats each of the five main action components (key, whippen, jack, repetition lever, and hammer) as a rigid body. The action model also incorporates a contact model to determine the normal and friction forces at 13 locations between each of the contacting bodies. All parameters in the model are directly measured from the physical properties of individual action components, allowing the model to be used as a prototyping tool for actions that have not yet been built. To test whether the model can accurately predict the behaviour of a piano action, an experimental apparatus was built. Based around a keyboard from a Boston grand piano, the apparatus uses an electric motor to actuate the key, a load cell to measure applied force, and optical encoders and a high speed video camera to measure the positions of the bodies. The apparatus was found to produce highly repeatable, reliable measurements of the action. The behaviour of the action model was compared to the measurements from the experimental apparatus for several types of key blows from a pianist. A qualitative comparison showed that the model could very accurately reproduce the behaviour of a real action for high force blows. When the forces were lower, the behaviour of the action model was still reasonable, but some discrepancy from the experimental results could be seen. In order to reduce the discrepancy, it was recommended that certain improvements could be made to the action model. Rigid bodies, most importantly the key and hammer, should be replaced with flexible bodies. The normal contact model should be modified to account for the speed-independent behaviour of felt compression. Felt bushings that are modelled as perfect revolute joints should instead be modelled as flexible contact surfaces.
12
Plested, Charles Paul. "Mechanism of action of seronegative myasthenia gravis". Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301392.
Pełny tekst źródła
13
Keane, Richard. "HPMA copolymer-aminoellipticine conjugates : mechanism of action". Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269617.
Pełny tekst źródła
14
Beecroft, Marikka Shannon. "Antimicrobial chelators and their mechanism of action". Thesis, Durham University, 2019. http://etheses.dur.ac.uk/12933/.
Pełny tekst źródłaStreszczenie:
Limiting the availability of metals in an environment is known to restrict bacterial growth and proliferation. For example, humans sequester metals to help prevent infection by pathogens, a system termed nutritional immunity. Chelators are small molecules that bind tightly to metals and thus have antibacterial properties that mimic these innate immune processes. This activity of chelators has not been studied extensively, although experiments with EDTA suggest that it disrupts bacterial membrane permeability by stripping lipopolysaccharide from the bacterial outer surface, possibly due to the stabilising Mg2+ and Ca2+. The work described here examines in detail the antibacterial effect of 11 chelators on Escherichia coli and how this relates to cellular starvation. Four distinct effects on cellular metal content were found with these chelators i) no change, ii) reduction to manganese, iii) reduction in zinc, and iv) reduction in iron combined with an increase in manganese. There was limited correlation between chelant metal affinities in solution with effects seen in cells. The chelants also exhibited variation in antibacterial efficacy, which was enhanced when used in combination, most yielding synergistic or additive effects. These chelants therefore offer significant potential as tools to probe metal homeostasis systems and as antibacterials. EDTA, DTPMP and Octopirox were studied further by screening their effects on growth using a selection of E. coli mutants. DTPMP and Octopirox have similar effects on cellular metal content, depriving cells of iron and inducing uptake of manganese; mutant data suggests that DTPMP primarily affects Fe3+ uptake, while Octopirox Fe2+. All three chelators also seem t have effects on oxidative damage and tolerance, especially EDTA which deprives cells of manganese. The E. coli transcriptional response to EDTA was also investigated by RNA-SEQ. EDTA has wide-ranging effects on cellular metabolism, upregulating genes involved in carbon utilisation, energy production, translation and transcriptional regulators, including some iron-sulphur cluster proteins. Overall, the results offer the first detailed insight into the antibacterial effect of a structurally diverse group of chelants and the first step in understanding the relationship between metal affinity and their antibacterial mechanisms of action.
15
Matkar, Smita S. "Mechanism of action of potential anticancer drugs". Scholarly Commons, 2008. https://scholarlycommons.pacific.edu/uop_etds/2368.
Pełny tekst źródłaStreszczenie:
Traditionally, inoperable or metastatic cancers have been treated by causing massive DNA damage in order to induce self-destruction (apoptosis) of the rapidly multiplying cancer cells. Initially, this strategy works for many cancers, in particular those which express normal p53 tumor suppressor protein. However, most cancers eventually aquire mutations in either p53 or other signaling molecules and fail to initiate apoptosis in response to severe DNA damage. During this study three types of compounds were investigated for their DNA damaging and anticancer effects: a pair of novel metal containing compounds, a pair of natural products, and a known synthetic drug which had been used many years ago for completely different indication. It was shown that all stop the growth of cancer cells and that the latter two classes do not require functional p53 because they work equally well in cells with normal (wildtype), mutant or no p53. The two nickel complexes investigated in this dissertation, differ in their ability to cause DNA damage and cell death. The oxidized form of the nickel complex, [Ni(CR-2H)] 2+ causes DNA damage and cell death at a much lower concentration than its reduced counterpart [Ni(CR)] 2+ . The phenanthridine alkaloids, Sanguinarine and Chelerythine cause high levels of DNA strand breaks and extremely rapid apoptosis which is not due to DNA damage because the quick onset precludes extensive signaling. The effects of the phenanthridines were linked to production of large amounts of reactive oxygen species (ROS), in particular hydrogen peroxide (H 2 O 2 ). The importance of ROS for the action of anticancer drugs as well as antibiotics is increasingly being recognized. In addition we also investigated the thioxanthone Lucanthone or Miracil D (which was used for the treatment of parasitic worms more than 50 years ago). It causes DNA strand breaks and apoptosis. Apoptosis occurs on a timescale consistent with signaling. However, p53 does not seem to be involved and alternative mechanisms are being investigated. This work provides new directions for designing novel anticancer drugs that are not subject to the limitations of DNA damaging agents.
16
Chant, Eleanor Laura. "The mechanism of action of ColE1 Rcd". Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613713.
Pełny tekst źródła
17
Jackson, Natalie Diane. "The mechanism of action of peroxygen biocides". Thesis, University of York, 1999. http://etheses.whiterose.ac.uk/9825/.
Pełny tekst źródła
18
Bagnobianchi, A. "The molecular mechanism of action of Bendamustine". Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1461456/.
Pełny tekst źródłaStreszczenie:
Bendamustine has demonstrated clinical efficacy in the treatment of haematological malignancies and distinguish itself from other alkylating agents. The mechanistic and clinical differences associated with Bendamustine may be related to its structural features including a benzimidazole ring, although the mechanism of action is poorly understood. Understanding the molecular mechanism of Bendamustine could explain the therapeutic efficacy and identify potential biomarkers for response. The Bendamustine-DNA interaction in naked DNA, cytotoxicity, and ICL formation and repair (unhooking) in naked DNA or in cell lines and patient multiple myeloma cells by the single cell gel electrophoresis (comet) assay, were analyzed. DNA damage response (DDR) and potential mechanisms of acquired resistance to Bendamustine were also evaluated. Bendamustine alkylated DNA at guanine-N7 positions, produced ICLs in naked DNA and in cells, and demonstrated a cytotoxic effect comparable to conventional ICL drugs (Cisplatin, Melphalan). However, ICLs were not efficiently repaired (unhooked) in A549 cells, which could repair Cisplatin or Melphalan ICLs. In plasma cells from both Non-Melphalan Treated or Melphalan Treated patients, no evidence of efficient repair of Bendamustine ICLs was observed. Bendamustine DDR compared to Cisplatin or Melphalan gave a more selective pattern of expression of genes involved in DNA damage signaling pathways, cells defective in ERCC1, XPF, and homologous recombination repair showed less sensitivity to Bendamustine, there were differences in ɣH2AX and RAD51 foci formation and cell cycle distributions. In derived acquired resistant cell lines, resistance was associated with a reduced level of ICL at an equimolar drug dose compared to the parental lines. The molecular mechanism of Bendamustine is similar to conventional alkylating agents: DNA alkylation and ICL formation. However, ICL repair inefficiency and altered DDR are the differences between Bendamustine and conventional alkylating agents due to its benzimidazole ring that influences, showed by G1/S arrest of cell cycle population, its mechanism.
19
Novikova, Natalia. "Mechanism of action of emergency contraceptive pill". Thesis, The University of Sydney, 2007. http://hdl.handle.net/2123/2151.
Pełny tekst źródłaStreszczenie:
The number of unwanted pregnancies has not decreased in recent years and this should be addressed. Emergency contraception may be effective when used correctly having the advantage that it can be used after an episode of unprotected sexual intercourse (when regular contraception has failed or was not used). In this research project I set out to explore some of the major reasons why there are still many unwanted pregnancies in Australia. I decided to focus on the use and non-use of emergency contraception, e.g. emergency contraception pill (ECP) “method failures” are not well understood because the actual mechanisms of action are still unclear. There is evidence ECP can effectively interfere with follicle growth and ovulation. It is much less clear is whether ECP is able to interfere with fertilization and implantation, in a way, which may make it acceptable to those who have strong religious beliefs in fertilization being the start of new life. Emergency contraception has the potential to prevent many unwanted pregnancies when unprotected intercourse has occurred. It has relatively high efficacy in many studies, but true method failures are not well understood. By contrast, many unwanted pregnancies occur for “social reasons” where emergency contraception has not been used. I set out to study changes in knowledge and usage of emergency contraception in these groups of Australian women seeking termination of pregnancy: 1. Before a dedicated emergency contraception pill (ECP) pack (Postinor) became available in Australia 2. One year after dedicated ECP became available on prescription 3. One year after the ECP pack became available “over the counter” without prescription. Ninety-nine women were recruited during their presentation with a request for ECP at the six Family Planning Clinics in Australia. All women took LNG 1.5mg in a single dose during the clinic consultation. A blood sample was taken immediately prior to ingestion of the ECP for estimation of serum LH, oestradiol and progesterone levels to calculate the day of the menstrual cycle. Based on these endocrine data we estimated the timing of ovulation to within a ±24-hour period with an accuracy of around 80%. Women were followed up 4-6 weeks later to ascertain pregnancy status. The effectiveness of ECP when taken before and after ovulation was determined. Three women in this study became pregnant despite taking the ECP (pregnancy rate 3%). All three women who became pregnant had unprotected intercourse between day -1 and 0 and took the ECP on day +2, based on endocrine data. Day zero was taken as ovulation day. Among seventeen women who had intercourse in the fertile period of the cycle and took the ECP after ovulation occurred (on day +1 to +2) we could have expected 3 or 4 pregnancies, based on Wilcox et al data. Three pregnancies were observed. Among 34 women who had intercourse on days –5 to –2 of the fertile period, and took ECP before or around ovulation, four pregnancies could have been expected, but none were observed. The major discrepancies between women’s self-report of stage of the cycle and the dating calculation based on endocrine data were observed in this study. These data are supportive of the concept that the LNG ECP has little or no effect on post-ovulation events, but is highly effective before ovulation. Our interpretation of the data in terms of timing of treatment relative to ovulation may explain why EC with LNG works sometimes and fails at other times. A larger study is needed to prove this hypothesis. To investigate other reasons for such a high rate of unwanted pregnancy, which probably has a larger impact we looked into womens knowledge of and attitude towards ECP. Seven hundred and eighteen women participated in this study by answering a questionnaire consisting of 15 questions on their demographic and reproductive characteristics as well as the knowledge about the ECP, e.g. 208 women were enrolled before the ECP was marketed in Australia in 2001, 308 after it was marketed and 202 after it became available over the counter (Group 1, 2, and 3, respectively). We found that the participants who have heard about ECP were significantly younger (p<0.005). The mean age of women who have never heard about of ECP was 29.8 years compared to 26.3 years in women who have heard about ECP. More women were aware about the ECP after it became available over the counter. Women in group 2 had higher educational level in comparison to women in group 2 and 3 (p<0.005). There was significant trend in increased use of ECP in women of higher educational level (p<0.005). The use of ECP did not increase significantly with improved availability and access to the ECP amongst women presenting for termination of pregnancy. Wider availability of he ECP pack in Australia and an easier access to it has increased women’s awareness about the ECP. However, the use of ECP has not increased. This study provides better understanding of mechanism of action of LNG ECP and an explanation to the method failure. It also reveals poor knowledge about ECP despite its wider availability and accessibility. Improving these is a worldwide challenge for family planners and all health professionals.
20
Novikova, Natalia. "Mechanism of action of emergency contraceptive pill". University of Sydney, 2007. http://hdl.handle.net/2123/2151.
Pełny tekst źródłaStreszczenie:
Master of MedicineThe number of unwanted pregnancies has not decreased in recent years and this should be addressed. Emergency contraception may be effective when used correctly having the advantage that it can be used after an episode of unprotected sexual intercourse (when regular contraception has failed or was not used). In this research project I set out to explore some of the major reasons why there are still many unwanted pregnancies in Australia. I decided to focus on the use and non-use of emergency contraception, e.g. emergency contraception pill (ECP) “method failures” are not well understood because the actual mechanisms of action are still unclear. There is evidence ECP can effectively interfere with follicle growth and ovulation. It is much less clear is whether ECP is able to interfere with fertilization and implantation, in a way, which may make it acceptable to those who have strong religious beliefs in fertilization being the start of new life. Emergency contraception has the potential to prevent many unwanted pregnancies when unprotected intercourse has occurred. It has relatively high efficacy in many studies, but true method failures are not well understood. By contrast, many unwanted pregnancies occur for “social reasons” where emergency contraception has not been used. I set out to study changes in knowledge and usage of emergency contraception in these groups of Australian women seeking termination of pregnancy: 1. Before a dedicated emergency contraception pill (ECP) pack (Postinor) became available in Australia 2. One year after dedicated ECP became available on prescription 3. One year after the ECP pack became available “over the counter” without prescription. Ninety-nine women were recruited during their presentation with a request for ECP at the six Family Planning Clinics in Australia. All women took LNG 1.5mg in a single dose during the clinic consultation. A blood sample was taken immediately prior to ingestion of the ECP for estimation of serum LH, oestradiol and progesterone levels to calculate the day of the menstrual cycle. Based on these endocrine data we estimated the timing of ovulation to within a ±24-hour period with an accuracy of around 80%. Women were followed up 4-6 weeks later to ascertain pregnancy status. The effectiveness of ECP when taken before and after ovulation was determined. Three women in this study became pregnant despite taking the ECP (pregnancy rate 3%). All three women who became pregnant had unprotected intercourse between day -1 and 0 and took the ECP on day +2, based on endocrine data. Day zero was taken as ovulation day. Among seventeen women who had intercourse in the fertile period of the cycle and took the ECP after ovulation occurred (on day +1 to +2) we could have expected 3 or 4 pregnancies, based on Wilcox et al data. Three pregnancies were observed. Among 34 women who had intercourse on days –5 to –2 of the fertile period, and took ECP before or around ovulation, four pregnancies could have been expected, but none were observed. The major discrepancies between women’s self-report of stage of the cycle and the dating calculation based on endocrine data were observed in this study. These data are supportive of the concept that the LNG ECP has little or no effect on post-ovulation events, but is highly effective before ovulation. Our interpretation of the data in terms of timing of treatment relative to ovulation may explain why EC with LNG works sometimes and fails at other times. A larger study is needed to prove this hypothesis. To investigate other reasons for such a high rate of unwanted pregnancy, which probably has a larger impact we looked into womens knowledge of and attitude towards ECP. Seven hundred and eighteen women participated in this study by answering a questionnaire consisting of 15 questions on their demographic and reproductive characteristics as well as the knowledge about the ECP, e.g. 208 women were enrolled before the ECP was marketed in Australia in 2001, 308 after it was marketed and 202 after it became available over the counter (Group 1, 2, and 3, respectively). We found that the participants who have heard about ECP were significantly younger (p<0.005). The mean age of women who have never heard about of ECP was 29.8 years compared to 26.3 years in women who have heard about ECP. More women were aware about the ECP after it became available over the counter. Women in group 2 had higher educational level in comparison to women in group 2 and 3 (p<0.005). There was significant trend in increased use of ECP in women of higher educational level (p<0.005). The use of ECP did not increase significantly with improved availability and access to the ECP amongst women presenting for termination of pregnancy. Wider availability of he ECP pack in Australia and an easier access to it has increased women’s awareness about the ECP. However, the use of ECP has not increased. This study provides better understanding of mechanism of action of LNG ECP and an explanation to the method failure. It also reveals poor knowledge about ECP despite its wider availability and accessibility. Improving these is a worldwide challenge for family planners and all health professionals.
21
Muraro, Lucia. "Studies of Botulinum Neurotoxins Mechanism of Action". Doctoral thesis, Università degli studi di Padova, 2009. http://hdl.handle.net/11577/3425607.
Pełny tekst źródłaStreszczenie:
Botulinum neurotoxins (7 serotypes of BoNTs, named from A to G) and tetanus neurotoxin (TeNT) are the most powerful clostridial toxins (CNTs). They are responsible for botulism and tetanus respectively. TeNT and BoNTs bind to peripheral nerve terminals and inhibit neurotransmitter release from presynaptic neuronal cells by proteolytic cleavage of proteins involved in the fusion of synaptic vesicles with the cell membrane. BoNTs act at the level of Peripheral Nervous System (PNS) causing flaccid paralysis whereas TeNT acts at the level of Central Nervous System (CNS) causing spastic paralysis. In particular BoNT A cleaves and disables SNAP25 (synaptosome-associated protein 25), impairing the release of acetylcholine at neuromuscular junction.
Structurally, CNTs are composed of two polypeptide chains linked by a single disulphide bond: the 50 kDa Light Chain (LC), which acts in the cytosol as a metalloprotease; and the 100 kDa Heavy chain, which includes a translocation domain (HN) and a receptor binding domain (HC). The three functional domains are structurally distinct and arranged in a linear fashion, such that there is no contact between the LC and HC domain. HC is further composed of two distinct subdomains HCN and HCC.
These neurotoxins act at femtomolar concentration and the high affinity binding is due to multiple binding sites, either for membrane ganglioside and neuronal specific membrane proteins. BoNT/A binds to SV2 (synaptic vesicle 2) and to the ganglioside GT1b. It was thought that these two binding sites were located one in HCN subdomain and the other in the HCC subdomain. HCN share some sequence homology with lectins so it was a good candidate to bind ganglioside. Recently by crystallographic analysis it has been shown that both the protein receptor and ganglioside sites of BoNT/B are in the HCC domain. Due to the high homology between all CNTs it is likely that also the SV2 and GT1b sites are in the BoNT A HCC domain. If this is the case the role of N-terminal subdomain of BoNT A is still unknown. The aim of this project is to investigate the role of HCN in the binding of BoNT A to the plasma membrane. It is important to notice that the sequence of this toxin portion is conserved among all CNTs.
The sequence of BoNT/A coding for the HCN domain (aa from 855 to 1093) has been cloned as His-Tag fusion protein, and fused to the Enhanced Green Fluorescent Protein (EGFP) and to the monomeric cherry red fluorescent protein (mCherry). By fluorescent microscopy observations we have shown that both the fluorescent chimera were able to bind to the plasma membrane of epithelial and neuronal cells. The fluorescent HCN domain remains at the plasma membrane during incubation times that allow the internalization of whole binding domain, HC. The fluorescent staining is not homogenous on the plasma membrane but is enriched in bright spots. For TeNT binding a role of lipid raft have been establish but for BoNTs the question seems to be still open. Ours data show that the sphingomyelin binding toxin lysenin, colocalized with HCN staining and treatment with sphingomyelinase diminished the HCN binding on epithelial cells. Moreover, in dot blot analysis HCN was able to directly interact with anionic lipid in particular phosphatidylinositol 5 phosphate (PI(5)P). A role for negative charged lipid in the binding of BoNTs and TeNT to lipid bilayer, it was already suggested; our hypothesis is that the N-terminal portion of the binding domain is able to bind anionic lipid in the environment of lipid raft. We suggest that these additional interactions with the membrane surface may play the role of positioning the toxin on the membrane surface ready for membrane insertion.
22
Davoodi, Jamshid. "Bacillus circulans xylanase: Stability and mechanism of action". Thesis, University of Ottawa (Canada), 1996. http://hdl.handle.net/10393/10216.
Pełny tekst źródłaStreszczenie:
The stability and mechanism of the action of the enzyme Bacillus circulans xylanase (1,4-$\beta$-D-xylanohydrolase, EC 3.2.1.8) were investigated by various biophysical techniques. On the basis of the sequence homology between B. circulans xylanase and xylanase A from Schizophyllum commune, a disulphide bond was introduced between the residues 100 and 148, S100C/N148C (DS1 mutant). The presence of this covalent cross-link leads to a 5$\sp\circ$C increase in the melting point of the protein, as verified by differential scanning calorimetry. Introduction of another disulphide bond in a similar position, V98C/A152C, the DS2 mutant also enhances the stability of the protein by as much as 4$\sp\circ$C. On the basis of the notion that the increase in the stability of a protein is proportional to the number of residues encompassed by the cross-link, the N and C-termini were joined, A1GC/G187,C188, to form the circular xylanase (cXI) mutant. This mutant also acquired a 3.8$\sp\circ$C elevated melting point. A combination of S100C/N148C and A1GC/G187,C188 mutations is accompanied by a 12.3$\sp\circ$C increase in the melting point, which is 3.5$\sp\circ$C more than expected. Thus, the stabilization effect of the two disulphide bonds appears to be cooperative rather than additive. Moreover, the thermodynamic data obtained from differential scanning calorimetry under reversible conditions support previous findings that the stabilizing effect of disulphide bonds is a consequence of a decreased conformational entropy of the unfolded state. Furthermore, the results of this study support the notion that the introduction of a disulphide bond can be used as a strategy to prevent the aggregation of proteins by restricting the exposure of some elements required for this process. The active site of Bacillus circulans xylanase contains two acidic residues, glutamic acids 78 and 172, which are crucial for the catalytic activity of the enzyme. Fourier-transform infrared and near-UV circular dichroism spectroscopies were used to determine the pK$\rm\sb{a}$ of these residues. For the wild type enzyme, a titration of one of carboxylate groups occurs at pH 6.8, as evidenced by FT-IR spectroscopy. This titration is absent in the E78Q of E172Q variants of the enzyme. This, taken with crystallographic data, indicates that glutamic acid at position 172 has an abnormally high pK$\rm\sb{a}$ of 6.8. The high pK$\rm\sb{a}$ value of Glu 172 is caused largely by electrostatic interactions of this residue with a proximal glutamic acid at position 78. Furthermore, the circular dichroism spectrum of the wild type xylanase shows a structural transition at pH 4.9 in the near-UV region which is absent for the E78C mutant. This taken with the fact that glutamic acid 78 forms a network of hydrogen bonds with tyrosine 69 and tryptophan 71 indicates that the transition with pK$\rm\sb{a}$ 4.9 should be attributed to glutamic acid 78. The presence of two proximal carboxyl groups, from glutamic acids 78 and 172, results in a pH-dependent destabilisation of the protein structure as evidenced by differential scanning calorimetry experiments, with the wild type xylanase and a number of mutant proteins.
23
Spiro, Simon George. "The mechanism of action of iminosugars as antiretrovirals". Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:7fc4ae01-bdec-49d0-afec-e0f3e9e8f41d.
Pełny tekst źródła
24
Rotjanapun, Kunjana. "Dietary components and cancer risk : mechanism of action". Thesis, University of Reading, 2017. http://centaur.reading.ac.uk/75144/.
Pełny tekst źródłaStreszczenie:
Colon cancer is the third most diagnosed type of cancer globally and prostate cancer is the most common type of cancer in men. Consumption of diets containing fruits and vegetables is associated with a reduction in risk of both types of cancer. This may be due to the presence of various beneficial bioactive compounds and micronutrients in these foods. The precise mechanism(s) of protection are not well characterised. In this thesis, I focused on the anti-cancer effect of blueberry polyphenols on models of colon and prostate cancer. I hypothesised that the parent phytochemicals present in blueberries and their metabolites generated by in vitro digestion and fermentation would suppress molecular pathways associated with the progression of prostate and colon cancer in cell culture based models of carcinogenesis. The human colon adenocarcinoma cell lines, HT-29 and CaCo-2, were used as colon cancer models. I found that delphinidin and malvidin and crude methanol/water blueberry extract reduced oxidative DNA damage (comet assay), inhibited growth (DAPI-staining), and suppressed cell cycle activity through G,/M arrest (PI/flow cytometry). No improvement in epithelial integrity (TER assay) were observed. The human cell lines, WPE1-NA22 and WPE1-NB26 were used to represent benign and advanced stages of prostate cancer respectively. Similarly, these findings demonstrated that delphinidin and malvidin and crude methanol/water blueberry extract reduced oxidative DNA damage (comet assay). These compounds also inhibited cell migration (wound healing assay). It should be noted that the metabolites from blueberry were less protective on prostate cancer than they were on the colon cancer cells The in vitro digestion and fermentation models do not fully represent the metabolic fate of phytochemicals in vivo. Therefore, ileal fluid samples were collected from ileostomy patients following consumption of raspberries and these samples were used in in vitro fermentation models to assess the production of bioactive phenolic acids in the colon from polyphenol precursors. The pattern of major phenolic acids formed by the micro biota, consisted of benzoic acid derivatives e.g. benzoic acid, 4-hydroxybenzoic acid and phenyl propionic acid derivatives e.g. 3-(phenyl) propionic acid, 3(3' -hydroxyphenyl) propionic acid and 3(4' -hydroxyphenyl) propionic acid. These observations were in agreement with previous findings from our collaborators. Considerable inter-individual variation in the distribution of phenolic acids was observed, possibly due to variable transit times along GIT and the physical condition of each volunteer. We found that theses benzoic acid dervatives protected against H,O,-induced DNA damage in CCD841, colon epithelial cells, suggesting a potential for these compounds to reduce the risk of DNA mutation in colon cells. Therefore, these breakdown products may provide a colonic health benefit; however, this requires further investigation. In the final part of the thesis as a minor objective, Selenium (Se) was investigated for its effect(s) on cell death and survival using the CaCo-2 human adenocarcinoma cell line. We hypothesised that Se may induce the expression of genes involved in endoplasmiC reticulum (ER) stress-induced apoptosis as measured by real-time qPCR. No evidence that Se significantly induced the expression of caspase 3, a key gene in the apoptotic pathway via ER stress pathway was found. Similarly, glutathione peroxidase 1, a detoxifying enzyme belonging in selenoprotein family was not significantly up-regulated after the treatment of physiologically-relevant concentrations of Se. In conclusion, the in vitro studies completed in this thesis with blueberry extract and its metabolites as well as the major individual berry anthocyanidins had preventative effects in colon and prostate cancer cell models through multiple mechanisms. Se also seems to be a potential candidate for cancer prevention in colon cell model; however, further research is necessary to clarify the mechanism of action. This thesis provides further mechanistic evidence for the protective effects of berry phenolics and their metabolites in reducing the risk of colon and prostate cancer.
25
Frith, Julie C. "Studies into the mechanism of action of clodronate". Thesis, University of Sheffield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299577.
Pełny tekst źródła
26
Martin, Duncan J. "Mechanism of action of the anticonvulsant drug gabapentin". Thesis, University of Aberdeen, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.395181.
Pełny tekst źródłaStreszczenie:
In this study, the whole-cell patch clamp technique and Fura-2 calcium (Ca2+) imaging techniques were employed to investigate the involvement of voltage activated calcium currents (VACCs) in the mechanism of action of the anticonvulsant drug gabapentin. Molecular biology studies were also carried out to assess which VACC subunits were required for drug sensitivity in particular cell cultures. Also investigated were the effects, if any, of gabapentin at GABA receptors and on cells of the F11 line. Voltage activated calcium currents were activated in cultured DRG neurones until a consistent current magnitude was achieved. Effects of gabapentin could then be measured by activation of subsequent currents in the presence of drug. The effects of various other compounds were also tested in this way, e.g. the effects of the related drug pregabalin, effects of the inhibitory neurotransmitter GABA, the effects of the GABAB antagonist saclofen and the effect of treating the cells with pertussis toxin. Gabapentin inhibited voltage activated calcium currents. This inhibition was voltage dependent but frequency independent. Gabapentin did not act at GABAA or GABAB receptors. Gabapentin effects were PTx sensitive suggesting a G-protein mechanism was involved. An experimental protocol for calcium fluorescence imaging was designed. This protocol allowed comparison of gabapentin and other drug effects against control responses, and is a protocol that could be used as an assay system to test the properties of compounds related to gabapentin. Gabapentin and pregabalin ((S)-isobutylgaba) both reduced the magnitude of evoked Ca2+ transients in both cultured DRG neurones and in F11 cells. The R-stereoisomer of pregabalin, PD-C, was shown to increase the magnitude of these transients. Both this increase and the decrease associated with gabapentin were PTx sensitive. These results indicate that gabapentin attenuates calcium currents at VACCs. The gabapentin binding site has been shown to be the α2δ subunit and it was observed that the activity of gabapentin is dependent on a G-protein linked mechanism and on the presence of modulatory VACC β subunits.
27
Churcher, Mark Jonathan. "Studies on the mechanism of action of Tat". Thesis, Open University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359975.
Pełny tekst źródła
28
Hurley, Laurence H. "Biosynthesis and mechanism of action of antitumor antibiotics". Thesis, University of Bath, 1996. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760690.
Pełny tekst źródła
29
Nawaz, Zafar. "Molecular Mechanism of Action of Steroid Hormone Receptors". Thesis, University of North Texas, 1992. https://digital.library.unt.edu/ark:/67531/metadc798398/.
Pełny tekst źródłaStreszczenie:
A novel bacterial expression system that is capable of producing high levels of soluble, stable, biologically active human vitamin D3 and estrogen receptors has been developed. The method utilizes ubiquitin fusion technology and a low temperature nalidixic acid induction of the lambda PL promoter. This system can produce large quantities of receptor antigen, but only a small fraction displays wild-type DNA and hormone binding properties. Therefore, the use of this system to overproduce receptors for crystallization studies is not practical. To overcome these problems, a 2 um based ubiquitin fusion system which allows regulated expression of the estrogen receptor in yeast (Saccharomyces cerevisiae) was developed. This system produces the estrogen receptor to a level of 0.2% of the total soluble protein. Moreover, this protein is undegradable, soluble, and biologically active. To test the transcriptional activity of the estrogen receptor produced in yeast, a cis-trans transcription assay was developed. This assay revealed that the transcriptional activity of the human estrogen receptor expressed in yeast was similar to that observed in transfected mammalian cells. This reconstituted estrogen transcription unit in Saccharomyces cerevisiae was utilized to examine the regulation of estrogen receptor functions by antiestrogens, to develop a random and rapid approach for identifying novel estrogen response elements, to characterize estrogen receptor variants cloned from human breast tumors, and to examine the effect of estrogen receptor on the regulation of osteocalcin gene.
30
Wong, Tin Lok. "Mechanism of action of silicon in cell signalling". Thesis, University of Cambridge, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709339.
Pełny tekst źródła
31
Pua, Khian Hong. "Investigating the Mechanism of Action of Sanglifehrin A". Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:17467488.
Pełny tekst źródłaStreszczenie:
Macrocyclic natural products occupy a special niche in the small molecule chemical space. Compared with other classes of small molecules, their larger size and conformational flexibility confer a higher propensity to recognize relatively flat surfaces that are predominant in protein-protein interactions. They are also thought to be the smallest examples of biomolecules that display functional sub-domains. Examples in this class of compounds are the immunosuppressants cyclosporine A (CSA), FK506, rapamycin (RAP) and sanglifehrin A (SFA) – the subject of this dissertation.
Aside from their therapeutic use in the clinic, immunosuppressants CSA, FK506, and RAP have also been proven to be indispensable tools for interrogating signal transduction pathways at the molecular level. These natural products have significantly contributed to our understanding of T cell signal transduction pathways and the molecular events involved in T cell activation. SFA is another immunosuppressive macrocyclic natural product that is structurally distinct from CSA but which, like CSA, binds to an abundant intracellular protein, cyclophilin A (PPIA) with high affinity. Unlike CSA, neither RAP nor SFA affect calcium-dependent IL-2 production. However, distinct from RAP, SFA does not inhibit mTOR. The molecular target of SFA and the cellular events resulting from its effect are still poorly understood. This dissertation describes efforts to identify the molecular target of SFA and tease apart its mode of action by enlisting a variety of target identification and validation approaches.Chemistry and Chemical Biology
32
Shrestha, Sanjib K. "Novel Aminoglycosides: Bioactive Properties and Mechanism of Action". DigitalCommons@USU, 2013. https://digitalcommons.usu.edu/etd/2073.
Pełny tekst źródłaStreszczenie:
Fungicide discovery is relatively neglected when compared to the investment in the development of antibacterial, antiviral, and anti-cancer therapeutics. Due to extensive use of currently available fungicides in agriculture and medicine, resistance is emerging among plant and animal pathogenic fungi. This necessitates the search for novel antifungal agents that are effective and less toxic and that do not promote resistance.
FG08 and K20 are novel aminoglycoside analogs synthesized from kanamycin B and A, respectively. The antimicrobial properties of these analogs were tested in vitro against a wide range of agriculturally and clinically important fungal pathogens. Both compounds showed broad-spectrum antifungal properties, but they did not inhibit bacteria such as Escherichia coli and Staphylococcus aureus. The hemolytic activities and cytotoxicities of FG08 and K20 were also evaluated. They showed no toxicity or lowered toxicity against animal cells at their antifungal minimum inhibitory concentrations (MICs).
The fungicidal mechanisms of action of FG08 and K20 were examined using intact cells of Saccharomyces cerevisiae, Cryptococcus neoformans, hyphae of Fusarium graminearum. FG08 and K20 caused SYTOX Green dye uptake and potassium efflux by intact cells, indicating that they increase plasma membrane permeability. FG08 and K20 also caused leakage of pre-loaded calcein from small unilamellar vesicles (SUVs) composed of lipids that mimic the lipid composition of fungal membranes, further suggesting increased membrane permeability as their mechanism of action.
The synergistic interactions of K20 with six azoles (such as itraconazole, and fluconazole) were investigated against a wide array of fungal pathogens. The in vitro results revealed strong synergy between K20 and azoles against plant and human pathogenic fungi. Their synergies were furthered confirmed by time kill curves and disk diffusion methods.
In conclusion, FG08 and K20 are broad-spectrum antifungal agents that do not inhibit bacteria. At their antifungal MICs, they are not toxic to animal cells, but they inhibit fungi by interacting with the fungal plasma membrane, leading to pore formation. These novel aminoglycoside analogs appear attractive for applications as fungicides in agriculture and medicine.
33
Ashraf, Sadia. "Study of mechanism of action of Scorpion neurotoxins". Doctoral thesis, Università degli studi di Padova, 2013. http://hdl.handle.net/11577/3423586.
Pełny tekst źródłaStreszczenie:
Summary
Scorpions are important representative of arthropods. They have been well adapted to the extremes of environmental conditions. Scorpions also play a vital role in ecological systems by maintaining balance between different populations in an ecosystem. Apart from their positive role scorpions are responsible for more than 1.2 million stings per year with almost 3000 deaths worldwide per year and thus posing serious threat to public health. Two families of scorpions i.e. Buthida and Hemiscorpiidae are dangerous for humans. Scorpion sting can result in mild effects of redness and pain to very severe and lethal effects which can result failure of multiple organs eventually leading to death.
Scorpion venom is composed of many different components such as low molecular weight peptides, nucleotides, lipids and certain enzymes. The diverse detrimental effects of scorpion sting result due to presence of many different types of toxins (neurotoxin, cardiotoxin, nephrotoxin, hemolytic toxin) and different enzymes (phosphodiesterases, phospholipases and hyaluronidases) in their venom. Since scorpions have a long evolutionary history during this long time period scorpions have developed a series of venom peptides that display a diverse range of biological functions.
The most widely studied components of scorpion venom are the ion channel-modulating toxins which have been studied and described in detail in literature. Antarease a new class of unique scorpion metalloproteases capable of cleaving SNARE proteins has been described only recently with no previous evidence on presence of such enzymes in scorpions. Up till now SNARE proteins have only been shown to be targets of clostridial neurotoxins. To investigate such a class of metalloproteases we have analyzed the action of different scorpion venoms both on recombinant SNARE proteins as well as in neuronal cell models.
Conclusion: This study shows for the first time the presence of antarease like proteins in scorpion species: Buthus eupeus and Orthochirus scrobiculosus. Both of the scorpion species contain active components i.e. metalloproteases that are able to cleave SNARE proteins in a mechanism similar to antarease.RIASSUNTO Gli Scorpioni sono importanti rappresentanti del phylum Artropodi. Essi si sono ben adattati a condizioni ambientali estreme e giocano un ruolo fondamentale in diversi ecosistemi. Allo stesso tempo gli scorpioni sono responsabili di più di 1.2 milioni di punture per anno con quasi 3000 morti in tutto il mondo. Sono due le famiglie di scorpioni pericolose per l’uomo: Buthida e Hemiscorpiidae. Le punture di scorpione possono causare da effetti lievi come rossore, e dolore a effetti gravi che causano danni a diversi organi ed eventualmente la morte del soggetto colpito. Il veleno di scorpione è costituito da diversi componenti come peptidi a basso peso molecolare, lipidi ed enzimi. Gli effetti patologici della puntura di scorpione sono causati dalla presenza di diverse tossine (neurotossina, cardiotossina, nefrotossina, tossina emolitica) e diversi enzimi (fosfodiesterasi, fosfolipasi, ialuronidasi) nel veleno. Dato che gli scorpioni hanno una lunga storia evolutiva, durante questo lungo periodo hanno sviluppato un serie di peptidi e proteine che possiedono diverse funzioni biologiche. Grazie alla loro abbondanza e quindi alla facilità d’isolamento, i componenti del veleno più studiati sono le tossine che esplicano la loro azione sui canali ionici i quali sono stati molto studiati e descritti in dettaglio in letteratura. Recentemente è stata descritta una nuova classe di metalloproteasi di scorpione capace di proteolizzare le proteine SNARE che è stata denominata Antarease. Fino ad ora le proteine SNARE che hanno un ruolo chiave nel processo di neuroesocitosi, sono state descritte essere il bersaglio molecolare solo di neurotossine batteriche quali le tossine del tetano e del botulismo. Per studiare questa nuova classe di metalloproteasi, abbiamo analizzato l’azione di diversi veleni di scorpioni sia su proteine SNARE ricombinanti sia su modelli di neuroni primari in coltura. Questo studio ha dimostrato la presenza di metalloproteasi simili all’Antarease in specie di scorpioni Buthus eupeus e Orthochirus scrobiculosus e che questi enzimi sono in grado di proteolizzare in maniera specifica le proteine SNARE.
34
Salazar, Montoya Vivian Angélica. "Exploring the mechanism of action of human antimicrobial ribonucleases". Doctoral thesis, Universitat Autònoma de Barcelona, 2015. http://hdl.handle.net/10803/310611.
Pełny tekst źródłaStreszczenie:
Las ribonucleases humanas son un grupo heterogéneo de proteínas pertenecientes a la
superfamilia de la Ribonucleasa A. Estas proteínas se caracterizan por su capacidad de
hidrolizar ácidos ribonucleicos y por la presencia de actividad antimicrobiana frente
diversos organismos patógenos como bacterias, hongos, parásitos y virus.
El primer objetivo del presente estudio doctoral se centra en la caracterización de la
actividad antimicrobiana y en modelos de membrana de las formas nativas de la
ribonucleasa 3 purificadas a partir de eosinófilos. Las distintas formas nativas presentan
modificaciones postraduccionales dadas por diversos grados de glicosilación que se
correlacionan con la activación de los eosinófilos durante los procesos inflamatorios. El
estudio establece la capacidad antimicrobiana de las formas nativas y su actividad en
modelos de membrana. Los resultados indican que las modificaciones
postrasduccionales modulan la actividad biológica de la RNasa 3, sugiriendo una
contribución in vivo en su función fisiológica.
Como segundo objetivo de esta tesis, se evaluó por primera vez en nuestro grupo de
investigación la actividad antimicótica de las ribonucleasas 3 y 7 frente al hongo
Candida albicans, el cual fue elegido como modelo patógeno eucariota. Se determinó y
caracterizó la presencia de actividad frente a Candida por parte de ambas ribonucleasas
humanas.
Por último, el tercer objetivo de esta tesis se centra en la purificación y caracterización
de la ribonucleasa 8, la más reciente ribonucleasa humana descrita, identificada
inicialmente en placenta. La RNasa 8 presenta un patrón inusual de enlaces disulfuro
respecto a sus proteínas homólogas. Este cambio estructural modifica la estabilidad de
la proteína y expone regiones que facilitan el proceso de agregación proteica. Fue
necesaria la previa optimización de un protocolo alternativo de purificación. Se
analizaron sus propiedades antimicrobianas, sugiriendo su posible participación en la
respuesta inmunitaria innata.
Los resultados del presente estudio corroboran las propiedades antimicrobianas de
diversas ribonucleasas humanas miembros de la familia de la RNasa A, sugiriendo una
función ancestral en el sistema de defensa innato. El estudio contribuye a la
comprensión de su mecanismo de acción y plantea su potencial uso como herramientas
terapéuticas.Human ribonucleases are a heterogeneous group of proteins belonging to the superfamily of RNase A. These proteins are characterized by their ability to hydrolyse ribonucleic acids and the presence of antimicrobial activity against various pathogens including bacteria, fungi, parasites and viruses. The first objective of this doctoral study is focused on the antimicrobial characterization of native Ribonuclease 3 forms purified from eosinophils. Native forms present posttranslational modifications giving different glycosylation grades that modulate their activity during inflammatory processes. This study aims to establish the antimicrobial properties of native forms purified from eosinophils and their activity in a membrane model system. Results indicate that post-translational modifications contribute to the the protein biological activities, suggesting a related physiological role. As a second objective, we evaluated for the first time the antifungal activity of the antimicrobial RNase 3 and RNase 7 against Candida albicans, an eukaryotic pathogen selected as a simple model to test the antimicrobial mechanism of action. Both human ribonucleases displayed a high antifungal activity. Results highlighted a dual mechanism of action, where cell lysis takes place at high protein concentration, while depolarization, cell internalization and cellular RNA degradation is achieved at sublethal doses. Finally, the last objective is focused on the characterization of ribonuclease 8, also called the placental RNase, the most recent human ribonuclease described. RNase 8 has gained and lost one cysteine residue in non-conserved positions in a mechanism called "disulphide shuffling". The protein tendency to aggregate required the design of an alternative purification protocol. We analysed its antimicrobial abilities, suggesting a possible role in innate defence. The results of this study confirmed the high antimicrobial activity of several human ribonucleases from the RNase A superfamily suggesting an ancestral role in the host immune defence response. The study contributed to the understanding of their mechanism of action and set the basis for applied drug design.
35
Sardari, Lodriche Soroush. "Natural antifungals, screening, isolation, synthesis, and mechanism of action". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0006/NQ29103.pdf.
Pełny tekst źródła
36
Pirola, Byron Antony. "Structure and mechanism of action of 5-aminolevulinate synthase /". Title page, table of contents and summary only, 1986. http://web4.library.adelaide.edu.au/theses/09PH/09php671.pdf.
Pełny tekst źródła
37
Barbara, Jeffrey A. J. "The mechanism of action of tumour necrosis factor-[alpha] /". Title page, contents and abstract only, 1995. http://web4.library.adelaide.edu.au/theses/09PH/09phb229.pdf.
Pełny tekst źródła
38
Massignani, Marzia. "Polymersomes for intracellular delivery : mechanism of action and applications". Thesis, University of Sheffield, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.555130.
Pełny tekst źródłaStreszczenie:
The cell cytosol and the different subcellular organelles house the most important biochemical processes that control cell functions. Effective delivery of bioactive agents within cells is expected to have an enormous impact on both gene therapy and the future development of new therapeutic and/or diagnostic strategies based on single cell bioactive agent interactions. The main aim of this project was the evaluation of pH sensitive polymersomes made of poly(2-(methacryloyloxy)ethyl phosphorylcholine)-poly(2- (diisopropylamino)ethyl methacrylate) (PMPC-PDPA) block copolymer as a potential vector for intracellular delivery applications. Upon internalization through endocytosis, polymersomes were demonstrated to disassemble, triggering an increase in osmotic pressure within the endosomal compartments. This increase in pressure temporally destabilizes the endosomal membrane and facilitated the release of the polymersome payload within the cell cytosol. Biocompatibility of polymersomes and their uptake kinetics by different cells (both primary cells and cell lines) were assessed by Confocal Laser Scanning Microscopy (CLSM), Transmission Electron Microscopy (TEM), Flow Cytometry and Fluorescence Spectroscopy. The cellular-uptake kinetics was strongly dependent on the polymersomes surface chemistry, size and surface topology. The latter is controlled by the extent of polymer-polymer phase separation within the external envelope of the polymersome. Polymersomes were also successfully used as efficient vectors for the delivery of DNA, functional proteins and different imaging probes.
39
Matthews, Charles S. "Investigations into the mechanism of action of antitumour quinols". Thesis, University of Nottingham, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.659198.
Pełny tekst źródłaStreszczenie:
Antitumour quinols containing the 4-hydroxycyclohexa-2,5-dienone pharmacophore potently inhibit human tumour cell growth in vitro and in vivo. This activity is postulated to occur via inhibition of the thioredoxin/thioredoxin reductase (TrxlTrxR) redox system which reduces numerous substrates involved in cellular proliferation, signal transduction, redox homeostasis and apoptosis. Similar to the archetypal quinol, PMX 464, its eventual successor, PMX 290, induced caspase-dependent apoptosis, cell cycle arrest and oxidative stress in sensitive tumour cells whilst depletion of glutathione increased tumour cell sensitivity to PMX 290. The ability of PMX 464 and PMX 290 to induce cellular responses understood to occur downstream of TrxlTrxR inhibition that could account for their antitumour activity were investigated. Quinol activity was shown to be independent of oxidative stress. Colon cancer cells stably overexpressing catalase retained sensitivity to PMX 464 and PMX 290 yet were resistant to hydrogen peroxide whilst the use of radical scavengers failed to abrogate quinol activity. Trx binds to and inhibits apoptosis signalling kinase 1 (ASK1), a mitogen activated protein kinase (MAPK) kinase kinase responsible for stress-induced apoptosis via sustained activation of the MAPKs c-jun N-terminal kinase (JNK) and p38. PMX 464 and PMX 290 disrupted cellular ASK1 :Trx1 complexes and induced sustained JNKlp38 phosphorylation yet overexpression of dominant negative ASK1 or pharmacological inhibition of JNKlp38 did not prevent quinol-induced apoptosis. Additionally, knockdown of Trx1 using siRNA did not impact quinol activity suggesting additional mechanisms of action. PMX 290 induced endoplasmic reticulum (ER) stress at apoptosis-inducing concentrations below those required to inhibit cellular TrxlTrxR. Upregulation of ER stress proteins, translation-inactivating phosphorylation events and ER distension occurred in response to PMX 290 alongside the accumulation/aggregation of ubiquitinated proteins prior to the onset of apoptosis. Proteasome inhibition was not responsible for these effects. A definitive cellular target for PMX 290 was not identified, however, useful tools have been generated which could be applied to investigate the actions of other redox homeostasis modulating therapies.
40
Lewis, John. "Mechanism of action of overbased additives in hydrocarbon media". Thesis, University of East Anglia, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280936.
Pełny tekst źródła
41
Watson, Jeannette Moira. "5-HT autoreceptors : pharmacological characterisation and mechanism of action". Thesis, University of Hertfordshire, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275119.
Pełny tekst źródła
42
Gudgeon, M. C. "Studies on the mechanism of action of cyclosporin A". Thesis, University of Sussex, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378279.
Pełny tekst źródła
43
Romero-Canelón, Isolda. "Design and mechanism of action of organometallic anticancer complexes". Thesis, University of Warwick, 2012. http://wrap.warwick.ac.uk/55211/.
Pełny tekst źródłaStreszczenie:
Since the discovery of cisplatin, numerous attempts have been made to emulate its activity while reducing its collateral toxicity. Coordination complexes based on a wide number of transition metals have been developed in the search for improved bioavailability, selectivity and reduced adverse side-effects. Ruthenium(II) complexes have been widely developed in this field as a viable alternative to platinum chemotherapeutics. This thesis is concerned with the synthesis, characterization and biological evaluation of three series of novel half-sandwich complexes of the general formula [RuII(arene)(X)(YZ)]n+. These piano-stool RuII complexes have been designed as to allow the fine-tuning of their chemical and biological properties. In the first two series, the arene unit has been varied between p-cymene, biphenyl and terphenyl to investigate the correlation between hydrophobicity and antiproliferative activity, while the N,N-imino pyridine chelating ligand, YZ, has been modified to include either a higher number of aromatic units that could allow better DNA intercalation or substituent groups that could affect the overall charge distribution in the complex. Finally, the monodentate ligand, X, is either chloride or iodide. These compounds have been fully characterised by NMR, MS and elemental analysis. Their aqueous behaviour has been investigated together with the extent of 9-EtG binding, as an indication of the possible interaction with nucleobases. The antiproliferative activity of these novel RuII complexes was determined, several of them show promising IC50 values, in the low μM range, against ovarian, colon, lung and breast cancer cell lines, in many cases the activities observed are better than cisplatin. The pathways for cellular accumulation were investigated. Complexes with an I as the monodentate ligand, X, exhibit partial energy-independent uptake. Overall results indicate that the novel RuII complexes synthesised in this thesis are most likely to be multi-targeted and that their mechanism of action depends to a great extent on the nature of the monodentate ligand, X. Two particularly active complexes in these series include the impy-NMe2 ligand as YZ chelate. These have been compared to their isostructural azopyridine analogues and also to their OsII equivalents. In this case, experiments were designed to study the activation of landmark events that lead to apoptosis, allowing contrasting the effects of different metal centres (Ru vs Os), isoelectronic ligands (impy-NMe2 vs azpy-NMe2) and monodentate ligands (Cl vs I). Results indicate that the molecular pathway followed by the iodido complexes is p53-independent. In comparison, the chlorido analogues activate the intrinsic apoptotic pathway and their activity relies on the existence of this tumour suppressor. DNA intercalation was also evaluated as a possible mechanism of action. Finally, the third series includes inactive RuII complexes with tetrahydroquinoline derivatives, which were found to enhance the activity of platinum drugs in clinical use. These promising preliminary results in the use of RuII complexes in combination therapy open a world of possibilities for the dose-reduction of platinum-chemotherapeutics.
44
Ooi, Nicola Chooi Twan. "Antibacterial activity and mechanism of action of lipophilic antioxidants". Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/5905/.
Pełny tekst źródłaStreszczenie:
The emergence and spread of antibiotic resistance hampers effective treatment of bacterial infections. This is particularly the case for infections involving a biofilm component, as the activity of existing antibacterial drugs against these surface-attached communities is limited. The work presented in this thesis sought to identify and characterise compounds with antibacterial and antibiofilm activity against the important pathogen, Staphylococcus aureus. Antistaphylococcal activity was assessed for 16 antioxidants that are used in cosmetics, traditional medicines or as food additives, and which have been reported previously to have some antibacterial activity. Initial experiments with tert-butylhydroquinone (TBHQ) showed that activity that had previously been ascribed to the antioxidant, was a consequence of its conversion to tert-butylbenzoquinone (TBBQ) under culture conditions. TBBQ displayed innate bactericidal activity against S. aureus that was effected through perturbation of the bacterial membrane. The other antioxidants also inhibited staphylococcal growth through perturbation of the cytoplasmic membrane, and compounds that displayed selective action against bacterial membranes were identified. Of the agents with bacterial specificity, TBBQ, celastrol and nordihydroguaiaretic acid (NDGA) also eradicated staphylococcal biofilms; a rare property amongst antibacterial agents. Although these antioxidants exhibited a similar membrane-damaging mode of action, their mechanisms of antibiofilm activity differed. TBBQ eradicated preformed biofilms through sterilisation of slow-growing and persister cell populations, whilst celastrol and NDGA caused physical disruption of the biofilm. All three antioxidants acted synergistically with gentamicin against biofilms, eradicating surface attached populations at concentrations that did not cause irritation or visible damage to a human skin equivalent. The potent and selective antibacterial activity, and low resistance potential upon extended subculture, suggest that these compounds could be used topically in combination with gentamicin to treat infected wounds.
45
Arafiles, Jan Vincent Valenzuela. "Macropinocytosis-Inducing Peptides: Identification, Utility, and Mechanism-of-Action". Kyoto University, 2020. http://hdl.handle.net/2433/259021.
Pełny tekst źródła
46
Slaughter, Alison Paige. "Mechanism of action of allosteric HIV-1 integrase inhibitors". The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1428684473.
Pełny tekst źródła
47
Vekariya, Rakesh. "TOWARDS UNDERSTANDING THE MECHANISM OF ACTION OF ABUSED CATHINONES". VCU Scholars Compass, 2012. http://scholarscompass.vcu.edu/etd/2841.
Pełny tekst źródłaStreszczenie:
The dopamine transporter (DAT) mediates reuptake of dopamine from the synaptic cleft into the presynaptic terminus and plays a critical role in maintaining the normal function of dopaminergic neurons. DAT is the major target of widely abused psychostimulant drugs, including cocaine and amphetamine. DAT also figures into disease states, and it is a target for therapeutic drugs. It is known that cathinone and methcathinone, β-keto analogs of amphetamine and methamphetamine, respectively, produce pharmacological actions similar to amphetamine. Cathinone and methcathinone analogs are recently gaining in popularity on the clandestine market (e.g. ‘bath salts’). Cathinone and methcathinone analogs as well as their amphetamine and methamphetamine counterparts were synthesized and examined at the hDAT expressed in Xenopus oocytes. One of the two major constituents of ‘bath salts’ (i.e., mephedrone) produced an electrophysiological signature similar to the dopamine releasing agent S(+)-amphetamine while the other major constituent (i.e., MDPV) produced an electrophysiological signature similar to the dopamine re-uptake inhibitor cocaine.
48
Deans, Bryan. "Studies on the mechanism of action on antitumour imidazotetrazinones". Thesis, Aston University, 1994. http://publications.aston.ac.uk/11048/.
Pełny tekst źródłaStreszczenie:
This thesis attempts to identify the cellular targets important to the cytotoxicity of imidazotetrazinones, to elucidate the pathways by which this damage leads to cell death, and to identify mechanisms by which tumour cells may circumvent this action. The levels of the DNA repair enzymes O6-alkylguanine-DNA-alkyltransferase (O6-AGAT) and 3-methyladenine-DNA-glycosylase (3MAG) have been examined in a range of murine and human cell lines with differential sensitivity to temozolomide. All the cell lines were proficient in 3MAG despite there being 40-fold difference in sensitivity to temozolomide. This suggests that while 3-methyladenine is a major product of temozolomide alkylation of DNA it is unlikely to be a cytotoxic lesion. In contrast, there was a 20-fold variation in O6-AGAT levels and the concentration of this repair enzyme correlated with variations in cytotoxicity. Furthermore, depletion of this enzyme in a resistant, O6-AGAT proficient cell line (Raji), by pre-treatment with the free base O6-methylguanine resulted in 54% sensitisation to the effects of temozolomide. These observations have been extended to 3 glioma cell lines; results that support the view that the cytotoxicity of temozolomide is related to alkylation at the O6-position of guanine and that resistance to this drug is determined by efficient repair of this lesion. It is clear, however, the other factors may influence tumour response since temozolomide showed little differential activity towards 3 established solid murine tumours in vivo, despite different tumour O6-AGAT levels.
49
Komaragiri, Shravan Kumar. "Mechanism of action of ID4 as a tumor suppressor". DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 2016. http://digitalcommons.auctr.edu/dissertations/3335.
Pełny tekst źródłaStreszczenie:
Initial studies demonstrated that Inhibitor of DNA binding/differentiation protein 4 (Id4) acts as a tumor suppressor in prostate cancer (PCa). To further confirm and investigate the mechanism by which ID4 acts as a tumor suppressor, herein we concentrated on two different approaches. In the first approach we investigated ID4 role as a tumor suppressor by regulating AKT/PI3K pathway. In the second approach, we examined the role ofld4 in blocking the tumorogenic properties of metastatic PC3 cells. Phosphoinositide 3-kinase/Protein kinase B (PB/AKT) pathway regulates multiple biological processes leading to cell survival, proliferation and growth in cancerous cells. We performed immunohistochemistry (IHC) to determine AKT, pAKT and PTEN protein expression in Id4 knockout mouse prostates and PCa cell lines. IHC on Id4 knockout mouse prostates demonstrated a significant decrease in PTEN expression as compared to normal mouse prostates. Consistent with decrease PTEN, the expression of pAKT expression increased. Similar pattern was observed in PCa cell lines: DU145 cells lacking Id4 had low PTEN as compared to ld4 over-expressing DU 145 cells. In addition, Chromatin immunoprecipitation (Ch!P) analysis also demonstrated an increase in the binding of acetylated p53 on PTEN promoter in the presence of Id4. The second approach demonstrated the tumor suppressor function of Id4 in highly tumorogenic and metastatic PC3 cell line. Interestingly, this study demonstrated that overexpression of Id4 in PC3 cells results in decreased tumorogenecity in part through increased expression of Androgen receptor (AR) and its target genes Cyclin dependent inhibitor I (p21) and FK506-binding protein 51 (FKBPS l ). Apoptosis, migration and cell proliferation decreased in the Id4 overexpressed PC3 cells. Mice injected with PC3 + Id4 cells showed decreased tumor size and volume. IHC studies on tumor xenografts demonstrated increased levels of AR, Ki67, and p21 in Id4 overexpressed xenograft. Collectively, our data indicate that 1D4 acts as tumor suppressor by regulating the levels of PTEN by prompting the binding ofacetylated p53 onto PTEN promoter which eventually results in inhibiting P13K/AKT pathway. Furthermore, Id4 not only increases the expression of AR in PC3 cells but also regulates the factors responsible for AR tumor suppressor activity.
50
Fan, Kit Man. "Studies on the molecular mechanism of action of artemisinins /". View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?CHEM%202008%20FAN.
Pełny tekst źródła