Artículos de revistas: "AROP"

1

Cosgriff, Angela J., Geoff Brasier, Jing Pi, Con Dogovski, Joseph P. Sarsero y A. J. Pittard. "A Study of AroP-PheP Chimeric Proteins and Identification of a Residue Involved in Tryptophan Transport". Journal of Bacteriology 182, n.º 8 (15 de abril de 2000): 2207–17. http://dx.doi.org/10.1128/jb.182.8.2207-2217.2000.

Texto completo

Resumen

ABSTRACT In vivo recombination has been used to make a series of AroP-PheP chimeric proteins. Analysis of their respective substrate profiles and activities has identified a small region within span III of AroP which can confer on a predominantly PheP protein the ability to transport tryptophan. Site-directed mutagenesis of the AroP-PheP chimera, PheP, and AroP has established that a key residue involved in tryptophan transport is tyrosine at position 103 in AroP. Phenylalanine is the residue at the corresponding position in PheP. The use of PheP-specific antisera has shown that the inability of certain chimeras to transport any of the aromatic amino acids is not a result of instability or a failure to be inserted into the membrane. Site-directed mutagenesis has identified two significant AroP-specific residues, alanine 107 and valine 114, which are the direct cause of loss of transport activity in chimeras such as A152P. These residues replace a glycine and an alanine in PheP and flank a highly conserved glutamate at position 110. Some suggestions are made as to the possible functions of these residues in the tertiary structure of the proteins.

Los estilos APA, Harvard, Vancouver, ISO, etc.

2

Dwivedi, Anamika, Deepak Dwivedi, Sujata Lakhtakia y Chalisgaonkar Charudutt. "Anatomical outcome of laser treatment alone in aggressive retinopathy of prematurity". Oman Journal of Ophthalmology 17, n.º 1 (2024): 37–42. http://dx.doi.org/10.4103/ojo.ojo_222_22.

Texto completo

Resumen

Abstract PURPOSE: The purpose is to study the anatomical outcome of eyes in aggressive retinopathy of prematurity (AROP), treated with laser photocoagulation alone and to evaluate factors affecting outcomes. METHODS: Records of consecutive babies diagnosed with AROP, undergoing laser photocoagulation treatment in rural tertiary care centers from October 2016 to January 2021 were reviewed retrospectively. Anatomical outcome at 6 months follow-up was grouped as good in eyes with complete regression and poor in those who developed retinal detachment (stage IV a, IV b, and V). Both groups were compared with respect to the period of gestation, birth weight (BW), age at screening, age at treatment, zone of disease, presence of retinal fibrovascular proliferation (FVP), tunica vasculosa lentis, preretinal bleed, need for supplement laser, and associated systemic risk factors. RESULTS: Of the total of 2468 babies screened, 124 (5.02%) were diagnosed with severe retinopathy of prematurity (ROP), of which 54 (43.5%) lasered AROP babies were analyzed. Mean BW and gestation period of the AROP cohort were 1.43 kg and 31.1 weeks, respectively. Eighty-six eyes (79.6%) had good outcomes with laser photocoagulation alone. Posterior location of disease, presence of FVP, neonatal sepsis, shock, and late screening for ROP were found to be factors associated with poor outcomes. CONCLUSION: Adequate and timely treatment with laser photocoagulation in AROP can achieve good treatment outcomes in a significant proportion of babies. Although a combined approach using laser, anti-vascular endothelial growth factor and early vitrectomy is better, laser remains a viable treatment option in AROP, especially with limited resources and high risk of loss to follow-up.

Los estilos APA, Harvard, Vancouver, ISO, etc.

3

Sen, Parveen, Pramod Bhende y Puja Maitra. "Surgical outcomes in aggressive retinopathy of prematurity (AROP)-related retinal detachments". Indian Journal of Ophthalmology 71, n.º 11 (20 de octubre de 2023): 3454–59. http://dx.doi.org/10.4103/ijo.ijo_2999_22.

Texto completo

Resumen

Introduction: Aggressive retinopathy of prematurity (AROP) is a severe and progressive variant of retinopathy of prematurity (ROP) rapidly forming fibrous tissue extending from the disc toward the posterior lens surface progressing to Stage 5 disease without traversing the classical course that includes Stages 1 to 3. Since AROP behaves differently from type 1 ROP, this study was undertaken to evaluate the surgical outcome of AROP-related detachments. Methods: Retrospective analysis of data from electronic medical records of babies diagnosed with AROP-related detachments who underwent micro-incision vitrectomy surgery (MIVS) was included. The demographic data, details of primary intervention (laser and/or intravitreal bevacizumab), and surgery were noted. In a subset of patients, surgical intervention was planned early at the onset of fibrovascular tissue. Results: 43 eyes of 26 babies with median birth weight 1175 g and median gestational age of 29 weeks were analyzed. 42/43 eyes underwent primary intervention in form of laser and/or anti-VEGF injection before surgery. 41.8%, 25.5%, and 32.5% eyes progressed to stages 4A, 4B, and 5, respectively, requiring surgical intervention. 66% eyes underwent lensectomy and vitrectomy (LV), and 44% eyes underwent lens sparring vitrectomy (LSV). 58% eyes had attached macula. 44% eyes that had a relatively less vascular diseases had better anatomical outcome (P = 0.019). At final follow-up, 53.4% eyes followed or at least had light fixation, and 77.7% eyes undergoing LSV fixated and/or followed light compared to 33% for LV (P = 0.04). Conclusion: Challenges in AROP include rapid progression to advanced stages of ROP requiring close monitoring and multiple interventions. Surgeries for AROP have a favorable anatomical and functional outcome in 58% and 53%, respectively. Eyes undergoing lens sparing vitrectomy had better visual outcomes.

Los estilos APA, Harvard, Vancouver, ISO, etc.

4

Yomantas, Yurgis A. V., Irina L. Tokmakova, Natalya V. Gorshkova, Elena G. Abalakina, Svetlana M. Kazakova, Evgueni R. Gak y Sergey V. Mashko. "Aromatic Amino Acid Auxotrophs Constructed by Recombinant Marker Exchange in Methylophilus methylotrophus AS1 Cells Expressing the aroP-Encoded Transporter of Escherichia coli". Applied and Environmental Microbiology 76, n.º 1 (30 de octubre de 2009): 75–83. http://dx.doi.org/10.1128/aem.02217-09.

Texto completo

Resumen

ABSTRACT The isolation of auxotrophic mutants, which is a prerequisite for a substantial genetic analysis and metabolic engineering of obligate methylotrophs, remains a rather complicated task. We describe a novel method of constructing mutants of the bacterium Methylophilus methylotrophus AS1 that are auxotrophic for aromatic amino acids. The procedure begins with the Mu-driven integration of the Escherichia coli gene aroP, which encodes the common aromatic amino acid transporter, into the genome of M. methylotrophus. The resulting recombinant strain, with improved permeability to certain amino acids and their analogues, was used for mutagenesis. Mutagenesis was carried out by recombinant substitution of the target genes in the chromosome by linear DNA using the FLP-excisable marker flanked with cloned homologous arms longer than 1,000 bp. M. methylotrophus AS1 genes trpE, tyrA, pheA, and aroG were cloned in E. coli, sequenced, disrupted in vitro using a Kmr marker, and electroporated into an aroP carrier recipient strain. This approach led to the construction of a set of marker-less M. methylotrophus AS1 mutants auxotrophic for aromatic amino acids. Thus, introduction of foreign amino acid transporter genes appeared promising for the following isolation of desired auxotrophs on the basis of different methylotrophic bacteria.

Los estilos APA, Harvard, Vancouver, ISO, etc.

5

Giri, Chandan, Jen-Yu Chang, Pierre Canisius Mbarushimana y Paul A. Rupar. "The Anionic Polymerization of a tert-Butyl-Carboxylate-Activated Aziridine". Polymers 14, n.º 16 (10 de agosto de 2022): 3253. http://dx.doi.org/10.3390/polym14163253.

Texto completo

Resumen

N-Sulfonyl-activated aziridines are known to undergo anionic-ring-opening polymerizations (AROP) to form polysulfonyllaziridines. However, the post-polymerization deprotection of the sulfonyl groups from polysulfonyllaziridines remains challenging. In this report, the polymerization of tert-butyl aziridine-1-carboxylate (BocAz) is reported. BocAz has an electron-withdrawing tert-butyloxycarbonyl (BOC) group on the aziridine nitrogen. The BOC group activates the aziridine for AROP and allows the synthesis of low-molecular-weight poly(BocAz) chains. A 13C NMR spectroscopic analysis of poly(BocAz) suggested that the polymer is linear. The attainable molecular weight of poly(BocAz) is limited by the poor solubility of poly(BocAz) in AROP-compatible solvents. The deprotection of poly(BocAz) using trifluoroacetic acid (TFA) cleanly produces linear polyethyleneimine. Overall, these results suggest that carbonyl groups, such as BOC, can play a larger role in the in the activation of aziridines in anionic polymerization and in the synthesis of polyimines.

Los estilos APA, Harvard, Vancouver, ISO, etc.

6

Ruggeri, Arianna, Anne Arvola, Antonella Samoggia y Vaiva Hendrixson. "Food behaviours of Italian consumers at risk of poverty". British Food Journal 117, n.º 11 (2 de noviembre de 2015): 2831–48. http://dx.doi.org/10.1108/bfj-12-2014-0417.

Texto completo

Resumen

Purpose – At a European level, Italy experiences one of the highest percentages of population at risk of poverty (AROP). However, studies on this consumer segment are scarce. The purpose of this paper is to investigate the food behaviours of Italian female consumers, distinguishing similarities and differences due to age and level of income. Design/methodology/approach – The investigation adopted an inductive approach in order to analyse and confirm the determinants of food behaviours. Data were collected through four focus groups. Data elaboration included content analyses with term frequency – inverse document frequency index and multidimensional scaling technique. Findings – The food behaviours of Italian female consumers are based on a common set of semantic categories and theoretical dimensions that are coherent with those applied by previous studies. The age of consumers impacts the relevance attributed to the categories and income contributes to the explanation of the conceptual relations among the categories that determine food behaviours. The approach to food of younger and mature consumers AROP is strongly driven by constraints such as price and time. The study did not confirm a link between a poor health attitude and low socio-economic status. Research limitations/implications – The outcomes achieved can be strengthened by quantitative analyses to characterise the relations occurring among the factors and dimensions that influence the food behaviours of consumers AROP. Originality/value – The study increases knowledge about Italian female consumers and provides an initial contribution to the analysis of the food behaviour of the population AROP.

Los estilos APA, Harvard, Vancouver, ISO, etc.

7

Hughes, K. T., J. R. Roth y B. M. Olivera. "A genetic characterization of the nadC gene of Salmonella typhimurium." Genetics 127, n.º 4 (1 de abril de 1991): 657–70. http://dx.doi.org/10.1093/genetics/127.4.657.

Texto completo

Resumen

Abstract The nadC gene of Salmonella encodes the pyridine biosynthetic enzyme PRPP-quinolinate phosphoribosyltransferase. Using a combination of genetic techniques, a deletion map for the Salmonella nadC gene has been generated which includes over 100 point mutants and 18 deletion intervals. The nadC alleles obtained by hydroxylamine mutagenesis include those suppressed by either amber, ochre, or UGA nonsense suppressors as well as alleles suppressed by the missense suppressor, sumA. Deletions were obtained by three separate protocols including spontaneous selection for loss of the nearby aroP gene, recombination between aroP::MudA and nadC::MudA insertion alleles, and selection for spontaneous loss of tetracycline resistance in a nearby guaC::Tn10dTc insertion mutant allele. The nadC mutants comprise one complementation group and the nadC+ allele is dominant to simple, nadC auxotrophic mutant alleles. Intragenic complementation of two nadC alleles, nadC493 and nadC494, mapping to deletion intervals 17 and 18, respectively, suggests that nadC encodes a multimeric enzyme. Both nadC and the nearby aroP locus are transcribed counterclockwise on the standard genetic map of Salmonella, in opposite orientation to the direction of chromosome replication.

Los estilos APA, Harvard, Vancouver, ISO, etc.

8

Yang, Ji, Peixiang Wang y A. J. Pittard. "Mechanism of Repression of the aroP P2 Promoter by the TyrR Protein of Escherichia coli". Journal of Bacteriology 181, n.º 20 (15 de octubre de 1999): 6411–18. http://dx.doi.org/10.1128/jb.181.20.6411-6418.1999.

Texto completo

Resumen

ABSTRACT Previously, we have shown that expression of the Escherichia coli aroP P2 promoter is partially repressed by the TyrR protein alone and strongly repressed by the TyrR protein in the presence of the coeffector tyrosine or phenylalanine (P. Wang, J. Yang, and A. J. Pittard, J. Bacteriol. 179:4206–4212, 1997). Here we present in vitro results showing that the TyrR protein and RNA polymerase can bind simultaneously to the aroP P2 promoter. In the presence of tyrosine, the TyrR protein inhibits open complex formation at the P2 promoter, whereas in the absence of any coeffector or in the presence of phenylalanine, the TyrR protein inhibits a step(s) following the formation of open complexes. We also present mutational evidence which implicates the N-terminal domain of the TyrR protein in the repression of P2 expression. The TyrR binding site of aroP, which includes one weak and one strong TyrR box, is located 5 bp downstream of the transcription start site of P2. Results from a mutational analysis show that the strong box (which is located more closely to the P2 promoter), but not the weak box, plays a critical role in P2 repression.

Los estilos APA, Harvard, Vancouver, ISO, etc.

9

Cuneo, G., C. Cesarini, D. Cianfrini y B. Gambi. "Osteopetrosi autosomica recessiva Diagnosi neonatale". Rivista di Neuroradiologia 15, n.º 6 (diciembre de 2002): 757–62. http://dx.doi.org/10.1177/197140090201500615.

Texto completo

Resumen

Le osteopetrosi sono un raro gruppo eterogeneo di condizioni patologiche, caratterizzate da aumento della densità dell'osso dovuto ad un disordine del riassorbimento da parte degli osteoclasti. Esse sono più frequenti in gruppi etnici all'interno dei quali sono presenti consanguinei. Ne sono state descritte almeno cinque tipi, ma le forme più note sono la autosomica recessiva (AROP, detta anche maligna), la intermedia (IOP, anch'essa recessiva ma con insorgenza più tardiva), la forma con acidosi tubulare e la autosomica dominante (ADOP). Riportiamo un caso di AROP diagnosticato in epoca neonatale (3 settimane). Esso dimostra come alcune caratteristiche radiologiche (ma non tutte), siano già presenti alla nascita. Alla luce delle recenti acquisizioni terapeutiche (soprattutto trapianto di cellule staminali), una diagnosi precoce della malattia potrebbe, pertanto, prevenire importanti modificazioni patologiche alcune delle quali gravemente invalidanti.

Los estilos APA, Harvard, Vancouver, ISO, etc.

10

Wang, Peixiang, Ji Yang, Akira Ishihama y A. J. Pittard. "Demonstration that the TyrR Protein and RNA Polymerase Complex Formed at the Divergent P3 Promoter Inhibits Binding of RNA Polymerase to the Major Promoter, P1, of the aroP Gene ofEscherichia coli". Journal of Bacteriology 180, n.º 20 (15 de octubre de 1998): 5466–72. http://dx.doi.org/10.1128/jb.180.20.5466-5472.1998.

Texto completo

Resumen

ABSTRACT In previous studies, we have identified three promoters (P1, P2, and P3) in the regulatory region of the Escherichia coli aroP gene (P. Wang, J. Yang, and A. J. Pittard, J. Bacteriol. 179:4206–4212, 1997). Both P1 and P2 can direct mRNA synthesis for aroP expression, whereas P3 is a divergent promoter which overlaps with P1. The repression of transcription from the major promoter, P1, has been postulated to involve the activation of the divergent promoter, P3, by the TyrR protein (P. Wang, J. Yang, B. Lawley, and A. J. Pittard, J. Bacteriol. 179:4213–4218, 1997). In the present study, we confirmed the proposed mechanism of P3-mediated repression of P1 transcription by studying the binding of RNA polymerase to the promoters P1 and P3 in vitro in the presence and absence of TyrR protein and its cofactors. Our results show that (i) only one RNA polymerase molecule can bind to the DNA fragment carrying the aroP regulatory region, (ii) RNA polymerase has a higher affinity for P1 than for either P2 or P3 and binds to P1 in the absence of TyrR protein, (iii) in the presence of TyrR protein and its cofactor, phenylalanine or tyrosine, RNA polymerase preferentially binds to P3, and (iv) RNA polymerase does not respond to the activation-defective mutant TyrR protein TyrR-RQ10 and remains bound to P1 in the presence of TyrR-RQ10 and either of the cofactors.

Los estilos APA, Harvard, Vancouver, ISO, etc.

11

Meisner, Quinton J., Sisi Jiang, Pengfei Cao, Tobias Glossmann, Andreas Hintennach y Zhengcheng Zhang. "An in situ generated polymer electrolyte via anionic ring-opening polymerization for lithium–sulfur batteries". Journal of Materials Chemistry A 9, n.º 46 (2021): 25927–33. http://dx.doi.org/10.1039/d1ta08244b.

Texto completo

Resumen

Solid polymer electrolytes were synthesized for Li–S battery via in situ anionic ring-opening polymerization (AROP) of an episulfide monomer initiated by the nucleophilic lithium sulfides/polysulfides which are generated during the initial discharge cycle.

Los estilos APA, Harvard, Vancouver, ISO, etc.

12

Raymond, Mary y Steve Parker. "Initial and medial geminate trills in Arop-Lokep". Journal of the International Phonetic Association 35, n.º 1 (16 de junio de 2005): 99–111. http://dx.doi.org/10.1017/s002510030500188x.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

13

Stritzker, Jochen, Jozef Janda, Christoph Schoen, Marcus Taupp, Sabine Pilgrim, Ivaylo Gentschev, Peter Schreier, Gernot Geginat y Werner Goebel. "Growth, Virulence, and Immunogenicity of Listeria monocytogenes aro Mutants". Infection and Immunity 72, n.º 10 (octubre de 2004): 5622–29. http://dx.doi.org/10.1128/iai.72.10.5622-5629.2004.

Texto completo

Resumen

ABSTRACT Mutants of Listeria monocytogenes with deletions in genes of the common branch of the biosynthesis pathway leading to aromatic compounds were constructed as possible virulence-attenuated carrier strains for protein antigens or vaccine DNA. aroA, aroB, and in particular aroE mutants showed strongly reduced growth rates in epithelial cells and even in rich culture media. The metabolism of the aro mutants under these conditions was predominantly anaerobic. Aerobic metabolism and a wild-type growth rate were, however, regained upon the addition of vitamin K2, suggesting that the aro mutants are deficient in oxidative respiration due to the lack of menaquinone. Replication of the aro mutants in the host cell's cytosol and cell-to-cell spread were drastically slowed down, and all aro mutants showed high virulence attenuation in mice, i.e., the 50% lethal dose in BALB/c mice was increased at least 104-fold for the aroA, aroB, and aroA/B mutants and >105-fold for the aroE mutant compared to the parent strain. Nevertheless, mice preimmunized with aro mutant bacteria elicited good T-cell response and full protection against a subsequent challenge with the virulent wild-type strain. A total of 5 × 106 aroA, aroB, and aroA/B mutant bacteria were sufficient to obtain a protective T-cell response, while 5 × 108 aroE or aroA/E mutants were necessary to achieve comparable numbers of antigen-specific T cells. These numbers were well tolerated without causing any signs of disease, indicating that Listeria strains with deletions in genes of the basic branch of the aromatic amino acid pathway could be useful vaccine carriers for inducing T-cell immunity.

Los estilos APA, Harvard, Vancouver, ISO, etc.

14

Cersini, Antonella, Anna Maria Salvia y Maria Lina Bernardini. "Intracellular Multiplication and Virulence of Shigella flexneri Auxotrophic Mutants". Infection and Immunity 66, n.º 2 (1 de febrero de 1998): 549–57. http://dx.doi.org/10.1128/iai.66.2.549-557.1998.

Texto completo

Resumen

ABSTRACT We have constructed and analyzed a group of Shigella flexneri 5 auxotrophic mutants. The wild-type strain M90T was mutagenized in genes encoding enzymes involved in the synthesis of (i) aromatic amino acids, (ii) nucleotides, and (iii) diaminopimelic acid. In this way, strains with single (aroB, aroC,aroD, purE, thyA, anddapB) and double (purE aroB, purE aroC, purE aroD, purE thyA) mutations were obtained. Although the Aro mutants had the same nutritional requirements when grown in laboratory media, they showed different degrees of virulence in vitro and in vivo. The aroB mutant was not significantly attenuated, whereas both the aroC andaroD strains were severely attenuated.p-Aminobenzoic acid (PABA) appeared to be the main requirement for the Aro mutants’ growth in tissue culture. Concerning nucleotides, thymine reduced the pathogenicity, whereas adenine did not. However, when combined with another virulence-affecting mutation, adenine auxotrophy appeared to potentiate that mutation’s effects. Consequently, the association of either the purE andaroC or the purE and aroD mutations had a great effect on virulence as measured by the Sereny test, whereas the purE aroB double mutation appeared to have only a small effect. All mutants except the dapB strain seemed to move within a Caco-2 cell monolayer after 3 h of infection. Nevertheless, the auxotrophs showing a high intracellular generation time were negative in the plaque assay. Knowledge of each mutation’s role in attenuating Shigella strains will provide useful tools in designing vaccine candidates.

Los estilos APA, Harvard, Vancouver, ISO, etc.

15

Elter, Johanna K., Jonas Eichhorn, Michael Ringleb y Felix H. Schacher. "Amine-containing diblock terpolymers via AROP: a versatile method for the generation of multifunctional micelles". Polymer Chemistry 12, n.º 27 (2021): 3900–3916. http://dx.doi.org/10.1039/d1py00666e.

Texto completo

Resumen

We herein report the synthesis and block copolymerization via AROP of three glycidyl amine species (PiGA; OPGA, and MPGA) with different hydrophobicity. Micelles formed from these block copolymers respond to changes in pH and H₂O₂ concentration.

Los estilos APA, Harvard, Vancouver, ISO, etc.

16

Çatiker, Efkan, Songül Kirlak, Mehmet Atakay y Bekir Salih. "Synthesis and characterization of novel poly(α-methyl β-alanine-b-lactone)s through hydrogen-transfer and ring-opening polymerization". Ovidius University Annals of Chemistry 33, n.º 1 (1 de enero de 2022): 78–83. http://dx.doi.org/10.2478/auoc-2022-0011.

Texto completo

Resumen

Abstract A series of novel poly(α-methyl β-alanine-b-lactone)s were prepared by a combination of hydrogen-transfer polymerization (HTP) of methacrylamide (MAm) and anionic ring-opening polymerization (AROP) of β-propiolactone (BPL), β-butyrolactone (BBL), and δ-valerolactone (DVL). For this purpose, poly(α-methyl β-alanine) (PmBA) having a living anionic end-group for a further extension was obtained via HTP of MAm. The anionic end-group on PmBA chains were used as initiation sites for AROP of BPL, BBL, and DVL. Fourier Transform Infrared Spectroscopy (FTIR) and Proton Nuclear Magnetic Resonance Spectroscopy (1H-NMR) confirmed the existence of both ester and α-methyl β-alanine (mBA) units in the final products. MALDI-MS analysis revealed that the poly(α-methyl β-alanine-b-lactone)s with average molar masses of several thousand g·mol−1 were obtained. DSC and TGA thermograms of each copolymer showed that the copolymers comprised the mBA and the corresponding ester units.

Los estilos APA, Harvard, Vancouver, ISO, etc.

17

Rihtar, Erik, Darja Žgur Bertok y Zdravko Podlesek. "The Uropathogenic Specific Protein Gene usp from Escherichia coli and Salmonella bongori is a Novel Member of the TyrR and H-NS Regulons". Microorganisms 8, n.º 3 (26 de febrero de 2020): 330. http://dx.doi.org/10.3390/microorganisms8030330.

Texto completo

Resumen

The Escherichia coli PAIusp is a small pathogenicity island encoding usp, for the uropathogenic specific protein (Usp), a genotoxin and three associated downstream imu1-3 genes that protect the producer against its own toxin. Bioinformatic analysis revealed the presence of the PAIusp also in publically available Salmonella bongori and Salmonella enterica subps. salamae genome sequences. PAIusp is in all examined sequences integrated within the aroP-pdhR chromosomal intergenic region. The focus of this work was identification of the usp promoter and regulatory elements controlling its activity. We show that, in both E. coli and S. bongori, the divergent TyrR regulated P3 promoter of the aroP gene, encoding an aromatic amino acid membrane transporter, drives usp transcription while H-NS acts antagonistically repressing expression. Our results show that the horizontally acquired PAIusp has integrated into the TyrR regulatory network and that environmental factors such as aromatic amino acids, temperature and urea induce usp expression.

Los estilos APA, Harvard, Vancouver, ISO, etc.

18

Lagarinhos, Joana, Sara Magalhães da Silva y José Martinho Oliveira. "Non-Isothermal Crystallization Kinetics of Polyamide 6/Graphene Nanoplatelets Nanocomposites Obtained via In Situ Polymerization: Effect of Nanofiller Size". Polymers 15, n.º 20 (17 de octubre de 2023): 4109. http://dx.doi.org/10.3390/polym15204109.

Texto completo

Resumen

Thermoplastic resin transfer molding (T-RTM) technology was applied to synthesize graphene nanoplatelets-based nanocomposites via anionic ring-opening polymerization (AROP). Polyamide 6 (PA6) was obtained by AROP and was used as the polymeric matrix of the developed nanocomposites. The non-isothermal crystallization behavior of PA6 and nanocomposites was analyzed by differential scanning calorimetry (DSC). Nanocomposites with 0.5 wt.% of graphene nanoplatelets (GNPs) with two different diameter sizes were prepared. Results have shown that the crystallization temperature shifted to higher values in the presence of GNPs. This behavior is more noticeable for the nanocomposite prepared with smaller GNPs (PA6/GN). The crystallization kinetic behavior of all samples was assessed by Avrami and Liu’s models. It was observed that GNPs increased the crystallization rate, thus revealing a nucleating ability, and also validated the reduction of half-time crystallization values. Such tendency was also supported by the lower activation energy values determined by Friedman’s method.

Los estilos APA, Harvard, Vancouver, ISO, etc.

19

Liu, Qian, Yongsong Cheng, Qingyang Xu, Xixian Xie y Ning Chen. "Effects of aroP gene disruption on L-tryptophan fermentation". Frontiers of Chemical Science and Engineering 6, n.º 2 (27 de mayo de 2012): 158–62. http://dx.doi.org/10.1007/s11705-012-1275-4.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

20

Sivaranjani, S., Jayanth Arun y Manavi D. Sindal. "Unilateral proliferative retinopathy in incontinentia pigmenti—An AROP mimicker". Indian Journal of Ophthalmology - Case Reports 3, n.º 4 (2023): 1230–31. http://dx.doi.org/10.4103/ijo.ijo_389_23.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

21

Belkhiri, Achraf, Nick Virgilio, Valérie Nassiet, Hélène Welemane, France Chabert y Olivier De Almeida. "Tailoring the Hydroxyl Density of Glass Surface for Anionic Ring-Opening Polymerization of Polyamide 6 to Manufacture Thermoplastic Composites". Polymers 14, n.º 17 (3 de septiembre de 2022): 3663. http://dx.doi.org/10.3390/polym14173663.

Texto completo

Resumen

Reactive thermoplastics matrices offer ease of processing using well-known molding techniques (such as Resin Transfer Molding) due to their initially low viscosity. For Polyamide 6 (PA6)/glass composites, the hydroxyl groups on the glass surface slow down the anionic ring-opening polymerization (AROP) reaction, and can ultimately inhibit it. This work aims to thoroughly control the hydroxyl groups and the surface chemistry of glass particulates to facilitate in situ AROP-an aspect that has been barely explored until now. A model system composed of a PA6 matrix synthesized by AROP is reinforced with calcinated and silanized glass microparticles. We systematically quantify, by TGA and FTIR, the complete particle surface modification sequence, from the dehydration, dehydroxylation and rehydroxylation processes, to the silanization step. Finally, the impact of the particle surface chemistry on the polymerization and crystallization of the PA6/glass composites was quantified by DSC. The results confirm that a careful balance is required between the dehydroxylation process, the simultaneous rehydroxylation and silane grafting, and the residual hydroxyl groups, in order to maintain fast polymerization and crystallization kinetics and to prevent reaction inhibition. Specifically, a hydroxyl concentration above 0.2 mmol OH·g−1 leads to a slowdown of the PA6 polymerization reaction. This reaction can be completely inhibited when the hydroxyl concentration reaches 0.77 mmol OH·g−1 as in the case of fully rehydroxylated particles or pristine raw particles. Furthermore, both the rehydroxylation and silanization processes can be realized simultaneously without any negative impact on the polymerization. This can be achieved with a silanization time of 2 h under the treatment conditions of the study. In this case, the silane agent gradually replaces the regenerated hydroxyls. This work provides a roadmap for the preparation of reinforced reactive thermoplastic materials.

Los estilos APA, Harvard, Vancouver, ISO, etc.

22

Zhu, Weipu, Mingjiang Zhong, Wenwen Li, Hongchen Dong y Krzysztof Matyjaszewski. "Clickable Stars by Combination of AROP and Aqueous AGET ATRP". Macromolecules 44, n.º 7 (12 de abril de 2011): 1920–26. http://dx.doi.org/10.1021/ma102704g.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

23

Ageyeva, Sibikin y Kovács. "A Review of Thermoplastic Resin Transfer Molding: Process Modeling and Simulation". Polymers 11, n.º 10 (24 de septiembre de 2019): 1555. http://dx.doi.org/10.3390/polym11101555.

Texto completo

Resumen

The production and consumption of polymer composites has grown continuously through recent decades and has topped 10 Mt/year. Until very recently, polymer composites almost exclusively had non-recyclable thermoset matrices. The growing amount of plastic, however, inevitably raises the issue of recycling and reuse. Therefore, recyclability has become of paramount importance in the composites industry. As a result, thermoplastics are coming to the forefront. Despite all their advantages, thermoplastics are difficult to use as the matrix of high-performance composites because their high viscosity complicates the impregnation process. A solution could be reactive thermoplastics, such as PA-6, which is synthesized from the ε-caprolactam (ε-CL) monomer via anionic ring opening polymerization (AROP). One of the fastest techniques to process PA-6 into advanced composites is thermoplastic resin transfer molding (T-RTM). Although nowadays T-RTM is close to commercial application, its optimization and control need further research and development, mainly assisted by modeling. This review summarizes recent progress in the modeling of the different aspects of the AROP of ε-CL. It covers the mathematical modeling of reaction kinetics, pressure-volume-temperature behavior, as well as simulation tools and approaches. Based on the research results so far, this review presents the current trends and could even plot the course for future research.

Los estilos APA, Harvard, Vancouver, ISO, etc.

24

TSUTSUMI, Masafumi y Takeshi CHISHAKI. "Time-series prediction system and AROP model in transportation demand analysis." Doboku Gakkai Ronbunshu, n.º 407 (1989): 17–26. http://dx.doi.org/10.2208/jscej.1989.407_17.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

25

Wang, P., J. Yang y A. J. Pittard. "Promoters and transcripts associated with the aroP gene of Escherichia coli." Journal of bacteriology 179, n.º 13 (1997): 4206–12. http://dx.doi.org/10.1128/jb.179.13.4206-4212.1997.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

26

Osváth, Zsófia, Anita Szőke, Szabolcs Pásztor, Györgyi Szarka, László Balázs Závoczki y Béla Iván. "Post-Polymerization Heat Effect in the Production of Polyamide 6 by Bulk Quasiliving Anionic Ring-Opening Polymerization of ε-Caprolactam with Industrial Components: A Green Processing Technique". Processes 8, n.º 7 (17 de julio de 2020): 856. http://dx.doi.org/10.3390/pr8070856.

Texto completo

Resumen

Bulk, solventless anionic ring-opening polymerization (AROP) of ε-caprolactam (CPL) with high yields, without side products and with short reaction times, initiated by caprolactamate-carbamoylcaprolactam initiating systems belong to green polymerization processes, leading to poly(ε-caprolactam) (Polyamide 6, PA6, Nylon 6). However, the effect of post-polymerization heat (i.e., slow, technically feasible cooling) on the fundamental characteristics of the resulting polymers such as yield and molecular weight distributions (MWDs) have not been revealed thus far. Significant post-polymerization effect was found by us in terms of both monomer conversions and MWDs by carrying out CPL polymerization with industrial components under conditions mimicking thermoplastic reaction transfer molding (T-RTM). Remarkably, higher monomer conversions and molecular weights (MWs) were obtained for Polyamide 6 samples prepared without quenching than that for the quenched polymers at the same reaction times. Independent of quenching or non-quenching, Mn of the resulting polymers as a function of conversion fell in the theoretical line of quasiliving AROP of CPL. At high monomer conversions, significant increase of the MW and broadening of the MWDs occurred, indicating pronounced chain–chain coupling. These findings have fundamental importance for designing processing conditions for in situ polymerization processes of ε-caprolactam by various techniques such as T-RTM, reaction injection molding (RIM), and other processing methods of Polyamide 6.

Los estilos APA, Harvard, Vancouver, ISO, etc.

27

So, Jae Il, Chung Soo Lee, Ji Young Jung, Jaewon Lee, Jin Kyu Choi, Sang Eun Shim y Yingjie Qian. "Optimization and Characterization of the F-LSR Manufacturing Process Using Quaternary Ammonium Silanolate as an Initiator for Synthesizing Fluorosilicone". Polymers 14, n.º 24 (15 de diciembre de 2022): 5502. http://dx.doi.org/10.3390/polym14245502.

Texto completo

Resumen

Due to the growing demand for versatile hybrid materials that can withstand harsh conditions (below −40 °C), fluorosilicone copolymers are becoming promising materials that can overcome the limited operating temperature of conventional rubber. In order to synthesize a fluorosilicone copolymer, a potent initiator capable of simultaneously initiating various siloxane monomers in anionic ring-opening polymerization (AROP) is required. In this study, tetramethyl ammonium silanolate (TMAS), a quaternary ammonium (QA) anion, was employed as an initiator for AROP, thereby fluoro-methyl-vinyl-silicone (FVMQ) and fluoro-hydrido-methyl-silicone (FHMQ) were successfully synthesized under optimized conditions. FT-IR, NMR, and GPC analyses confirmed that the chain length and functional group content of FVMQ and FHMQ are controlled by changing the ratio of the components. Moreover, fluorine-involved liquid silicone rubber (F-LSR) was prepared with FVMQ as the main chain and FHMQ as a crosslinker. The tensile strength, elongation, and hardness of each F-LSR sample were measured. Finally, it was confirmed through TGA, DSC, TR-test, and embrittlement testing that elastic retention at low temperatures improved even though the heat resistance slightly decreased as the trifluoropropyl group increased in F-LSR. We anticipate that the optimization of fluorosilicone synthesis initiated by QA and the comprehensive characterization of F-LSRs with different fluorine content and chain lengths will be pivotal to academia and industry.

Los estilos APA, Harvard, Vancouver, ISO, etc.

28

Wang, Songwei, Dongliang Liu, Muhammad Bilal, Wei Wang y Xuehong Zhang. "Uncovering the Role of PhzC as DAHP Synthase in Shikimate Pathway of Pseudomonas chlororaphis HT66". Biology 11, n.º 1 (6 de enero de 2022): 86. http://dx.doi.org/10.3390/biology11010086.

Texto completo

Resumen

DAHP synthase catalyzes the first step in the shikimate pathway, deriving the biosynthesis of aromatic amino acids (Trp, Phe and Tyr), phenazine-1-carboxamide, folic acid, and ubiquinone in Pseudomonas chlororaphis. In this study, we identified and characterized one DAHP synthase encoding gene phzC, which differs from the reported DAHP synthase encoding genes aroF, aroG and aroH in E. coli. PhzC accounts for approximately 90% of the total DAHP synthase activities in P. chlororaphis HT66 and plays the most critical role in four DAHP synthases in the shikimate pathway. Inactivation of phzC resulted in the reduction of PCN production by more than 90%, while the absence of genes aroF, aroG and aroH reduced PCN yield by less than 15%, and the production of PCN was restored after the complementation of gene phzC. Moreover, the results showed that phzC in P. chlororaphis HT66 is not sensitive to feedback inhibition. This study demonstrated that gene phzC is essential for PCN biosynthesis. The expression level of both phzC and phzE genes are not inhibited in feedback by PCN production due to the absence of a loop region required for allosteric control reaction. This study highlighted the importance of PhzC and applying P. chlororaphis for shikimate pathway-derived high-value biological production.

Los estilos APA, Harvard, Vancouver, ISO, etc.

29

Su, Panpan, Zhiwei Song, Guichun Wu, Yancun Zhao, Yuqiang Zhang, Bo Wang, Guoliang Qian, Zheng Qing Fu y Fengquan Liu. "Insights Into the Roles of Two Genes of the Histidine Biosynthesis Operon in Pathogenicity of Xanthomonas oryzae pv. oryzicola". Phytopathology® 108, n.º 5 (mayo de 2018): 542–51. http://dx.doi.org/10.1094/phyto-09-17-0332-r.

Texto completo

Resumen

Xanthomonas oryzae pv. oryzicola is an X. oryzae pathovar that causes bacterial leaf streak in rice. In this study, we performed functional characterization of a nine-gene his operon in X. oryzae pv. oryzicola. Sequence analysis indicates that this operon is highly conserved in Xanthomonas spp. Auxotrophic assays confirmed that the his operon was involved in histidine biosynthesis. We found that two genes within this operon, trpR and hisB, were required for virulence and bacterial growth in planta. Further research revealed that trpR and hisB play different roles in X. oryzae pv. oryzicola. The trpR acts as a transcriptional repressor and could negatively regulate the expression of hisG, -D, -C, -B, -H, -A, and -F. hisB, which encodes a bifunctional enzyme implicated in histidine biosynthesis, was shown to be required for xanthomonadin production in X. oryzae pv. oryzicola. The disruption of hisB reduced the transcriptional expression of five known shikimate pathway-related genes xanB2, aroE, aroA, aroC, and aroK. We found that the his operon in X. oryzae pv. oryzicola is not involved in hypersensitive response in nonhost tobacco plants. Collectively, our results revealed that two genes in histidine biosynthesis operon play an important role in the pathogenicity of X. oryzae pv. oryzicola Rs105.

Los estilos APA, Harvard, Vancouver, ISO, etc.

30

Cosgriff, A. J. y A. J. Pittard. "A topological model for the general aromatic amino acid permease, AroP, of Escherichia coli." Journal of bacteriology 179, n.º 10 (1997): 3317–23. http://dx.doi.org/10.1128/jb.179.10.3317-3323.1997.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

31

Wang, P., J. Yang, B. Lawley y A. J. Pittard. "Repression of the aroP gene of Escherichia coli involves activation of a divergent promoter." Journal of bacteriology 179, n.º 13 (1997): 4213–18. http://dx.doi.org/10.1128/jb.179.13.4213-4218.1997.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

32

Sebkova, Alena, Daniela Karasova, Magdalena Crhanova, Eva Budinska y Ivan Rychlik. "aro Mutations in Salmonella enterica Cause Defects in Cell Wall and Outer Membrane Integrity". Journal of Bacteriology 190, n.º 9 (29 de febrero de 2008): 3155–60. http://dx.doi.org/10.1128/jb.00053-08.

Texto completo

Resumen

ABSTRACT In this study we characterized aro mutants of Salmonella enterica serovars Enteritidis and Typhimurium, which are frequently used as live oral vaccines. We found that the aroA, aroD, and aroC mutants were sensitive to blood serum, albumen, EDTA, and ovotransferrin, and this defect could be complemented by an appropriate aro gene cloned in a plasmid. Subsequent microarray analysis of gene expression in the aroD mutant in serovar Typhimurium indicated that the reason for this sensitivity might be the upregulation of murA. To confirm this, we artificially overexpressed murA from a multicopy plasmid, and this overexpression caused sensitivity of the strain to albumen and EDTA but not to serum and ovotransferrin. We concluded that attenuation of aro mutants is caused not only by their inability to synthesize aromatic metabolites but also by their defect in cell wall and outer membrane functions associated with decreased resistance to components of innate immune response.

Los estilos APA, Harvard, Vancouver, ISO, etc.

33

Chye, M. L., J. R. Guest y J. Pittard. "Cloning of the aroP gene and identification of its product in Escherichia coli K-12." Journal of Bacteriology 167, n.º 2 (1986): 749–53. http://dx.doi.org/10.1128/jb.167.2.749-753.1986.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

34

Chye, M. L. y J. Pittard. "Transcription control of the aroP gene in Escherichia coli K-12: analysis of operator mutants." Journal of Bacteriology 169, n.º 1 (1987): 386–93. http://dx.doi.org/10.1128/jb.169.1.386-393.1987.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

35

Roberts, R. E., C. I. Lienhard, C. G. Gaines, J. M. Smith y J. R. Guest. "Genetic and molecular characterization of the guaC-nadC-aroP region of Escherichia coli K-12." Journal of Bacteriology 170, n.º 1 (1988): 463–67. http://dx.doi.org/10.1128/jb.170.1.463-467.1988.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

36

Zaikov, Gennady y Alexander Volod’kin. "Alkylation of 2,6-di-tert-Butylphenol with Methyl Acrylate Catalyzed by Potassium 2,6-di-tert-Butylphenoxide". Chemistry and Chemical Technology 4, n.º 2 (15 de junio de 2010): 101–5. http://dx.doi.org/10.23939/chcht04.02.101.

Texto completo

Resumen

The kinetics of catalytic alkylation of 2,6-di-tert-butylphenol (ArOH) with methyl acrylate (MA) in the presence of potassium 2,6-di-tert-butylphenoxide (ArOK) depends on the method for the preparation of ArOK. The reaction of ArOH with KOH at temperatures > 453 K affords monomeric ArOK, which properties differ from those in the case of potassium 2,6-di-tert-butylphenoxide synthesized by the earlier methods. The regularities of ArOH alkylation depend on the ArOK concentration, the ArOH:MA ratio, and the effect of microadditives of polar solvents.

Los estilos APA, Harvard, Vancouver, ISO, etc.

37

Paravicini, G., H. U. Mösch, T. Schmidheini y G. Braus. "The general control activator protein GCN4 is essential for a basal level of ARO3 gene expression in Saccharomyces cerevisiae". Molecular and Cellular Biology 9, n.º 1 (enero de 1989): 144–51. http://dx.doi.org/10.1128/mcb.9.1.144-151.1989.

Texto completo

Resumen

The ARO3 gene encodes one of two 3-deoxy-D-arabino-heptulosonate-7-phosphate isoenzymes in Saccharomyces cerevisiae catalyzing the first step in the biosynthesis of aromatic amino acids. The ARO3-encoded 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase (EC 4.1.2.15) is feedback inhibited by phenylalanine; its isoenzyme, the ARO4 gene product, is inhibited by tyrosine. Both genes ARO3 and ARO4 are strongly regulated under the general control regulatory system. Cells carrying only one intact isogene are phenotypically indistinguishable from a wild-type strain when grown on minimal medium. The complete functional ARO3 promoter comprises 231 base pairs and contains only one TGACTA binding site for the general control activator protein GCN4. Mutating this element to TTACTA inhibits binding of GCN4 and results in a decreased basal level of ARO3 gene product and slow growth of a strain defective in its isogene ARO4. In addition, ARO3 gene expression cannot be elevated under amino acid starvation conditions. An ARO3 aro4 strain with gcn4 genetic background has the same phenotype of low ARO3 gene expression and slow growth. The amount of GCN4 protein present in repressed wild-type cells therefore seems to contribute to a basal level of ARO3 gene expression. The general control activator GCN4 has thus two functions: (i) to maintain a basal level of ARO3 transcription (basal control) in the presence of amino acids and (ii) to derepress the ARO3 gene to a higher transcription rate under amino acid starvation (general control).

Los estilos APA, Harvard, Vancouver, ISO, etc.

38

Paravicini, G., H. U. Mösch, T. Schmidheini y G. Braus. "The general control activator protein GCN4 is essential for a basal level of ARO3 gene expression in Saccharomyces cerevisiae." Molecular and Cellular Biology 9, n.º 1 (enero de 1989): 144–51. http://dx.doi.org/10.1128/mcb.9.1.144.

Texto completo

Resumen

The ARO3 gene encodes one of two 3-deoxy-D-arabino-heptulosonate-7-phosphate isoenzymes in Saccharomyces cerevisiae catalyzing the first step in the biosynthesis of aromatic amino acids. The ARO3-encoded 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase (EC 4.1.2.15) is feedback inhibited by phenylalanine; its isoenzyme, the ARO4 gene product, is inhibited by tyrosine. Both genes ARO3 and ARO4 are strongly regulated under the general control regulatory system. Cells carrying only one intact isogene are phenotypically indistinguishable from a wild-type strain when grown on minimal medium. The complete functional ARO3 promoter comprises 231 base pairs and contains only one TGACTA binding site for the general control activator protein GCN4. Mutating this element to TTACTA inhibits binding of GCN4 and results in a decreased basal level of ARO3 gene product and slow growth of a strain defective in its isogene ARO4. In addition, ARO3 gene expression cannot be elevated under amino acid starvation conditions. An ARO3 aro4 strain with gcn4 genetic background has the same phenotype of low ARO3 gene expression and slow growth. The amount of GCN4 protein present in repressed wild-type cells therefore seems to contribute to a basal level of ARO3 gene expression. The general control activator GCN4 has thus two functions: (i) to maintain a basal level of ARO3 transcription (basal control) in the presence of amino acids and (ii) to derepress the ARO3 gene to a higher transcription rate under amino acid starvation (general control).

Los estilos APA, Harvard, Vancouver, ISO, etc.

39

Juminaga, Darmawi, Edward E. K. Baidoo, Alyssa M. Redding-Johanson, Tanveer S. Batth, Helcio Burd, Aindrila Mukhopadhyay, Christopher J. Petzold y Jay D. Keasling. "Modular Engineering of l-Tyrosine Production in Escherichia coli". Applied and Environmental Microbiology 78, n.º 1 (21 de octubre de 2011): 89–98. http://dx.doi.org/10.1128/aem.06017-11.

Texto completo

Resumen

ABSTRACTEfficient biosynthesis ofl-tyrosine from glucose is necessary to make biological production economically viable. To this end, we designed and constructed a modular biosynthetic pathway forl-tyrosine production inE. coliMG1655 by encoding the enzymes for converting erythrose-4-phosphate (E4P) and phosphoenolpyruvate (PEP) tol-tyrosine on two plasmids. Rational engineering to improvel-tyrosine production and to identify pathway bottlenecks was directed by targeted proteomics and metabolite profiling. The bottlenecks in the pathway were relieved by modifications in plasmid copy numbers, promoter strength, gene codon usage, and the placement of genes in operons. One major bottleneck was due to the bifunctional activities of quinate/shikimate dehydrogenase (YdiB), which caused accumulation of the intermediates dehydroquinate (DHQ) and dehydroshikimate (DHS) and the side product quinate; this bottleneck was relieved by replacing YdiB with its paralog AroE, resulting in the production of over 700 mg/liter of shikimate. Another bottleneck in shikimate production, due to low expression of the dehydroquinate synthase (AroB), was alleviated by optimizing the first 15 codons of the gene. Shikimate conversion tol-tyrosine was improved by replacing the shikimate kinase AroK with its isozyme, AroL, which effectively consumed all intermediates formed in the first half of the pathway. Guided by the protein and metabolite measurements, the best producer, consisting of two medium-copy-number, dual-operon plasmids, was optimized to produce >2 g/literl-tyrosine at 80% of the theoretical yield. This work demonstrates the utility of targeted proteomics and metabolite profiling in pathway construction and optimization, which should be applicable to other metabolic pathways.

Los estilos APA, Harvard, Vancouver, ISO, etc.

40

Moore, J. D., H. K. Lamb, T. Garbe, S. Servos, G. Dougan, I. G. Charles y A. R. Hawkins. "Inducible overproduction of the Aspergillus nidulans pentafunctional AROM protein and the type-I and -II 3-dehydroquinases from Salmonella typhi and Mycobacterium tuberculosis". Biochemical Journal 287, n.º 1 (1 de octubre de 1992): 173–81. http://dx.doi.org/10.1042/bj2870173.

Texto completo

Resumen

The aroQ gene of Mycobacterium tuberculosis, encoding a type-II 3-dehydroquinase, and the aroD gene of Salmonella typhi, encoding a type-I 3-dehydroquinase, have been highly overexpressed in Escherichia coli using the powerful trc promoter contained within the expression vector pKK233-2. The M. tuberculosis type-II 3-dehydroquinase has been purified in bulk from overproducing strains of E. coli to greater than 95% homogeneity. The protein is extremely heat-stable, is active as a homododecamer and has the lowest reported Km value of any type-II 3-dehydroquinase. The pentafunctional aromA gene of Aspergillus nidulans has been overexpressed more than 120-fold in an A. nidulans aromA- qutB- double mutant from a truncated quinate-inducible qutE promoter, such that the AROM protein is visible as a significant fraction (approx. 6%) in cell-free crude extracts. The M. tuberculosis aroQ gene has been fused to the same truncated qutE promoter and shown to encode quinate-inducible 3-dehydroquinase activity that allows a qutE- mutant strain of A. nidulans to utilize quinate as sole carbon source.

Los estilos APA, Harvard, Vancouver, ISO, etc.

41

Rodriguez, Sarah H., Anna L. Ells, Michael P. Blair, Parag K. Shah, C. Armitage Harper, Maria Ana Martinez-Castellanos, S. Grace Prakalapakorn et al. "Retinopathy of Prematurity in the 21st Century and the Complex Impact of Supplemental Oxygen". Journal of Clinical Medicine 12, n.º 3 (3 de febrero de 2023): 1228. http://dx.doi.org/10.3390/jcm12031228.

Texto completo

Resumen

Retinopathy of prematurity (ROP) is a leading cause of childhood blindness. Not only do the epidemiologic determinants and distributions of patients with ROP vary worldwide, but clinical differences have also been described. The Third Edition of the International Classification of ROP (ICROP3) acknowledges that aggressive ROP (AROP) can occur in larger preterm infants and involve areas of the more anterior retina, particularly in low-resource settings with unmonitored oxygen supplementation. As sub-specialty training programs are underway to address an epidemic of ROP in sub-Saharan Africa, recognizing characteristic retinal pathology in preterm infants exposed to unmonitored supplemental oxygen is important to proper diagnosis and treatment. This paper describes specific features associated with various ROP presentations: oxygen-induced retinopathy in animal models, traditional ROP seen in high-income countries with modern oxygen management, and ROP related to excessive oxygen supplementation in low- and middle-income countries: oxygen-associated ROP (OA-ROP).

Los estilos APA, Harvard, Vancouver, ISO, etc.

42

TSUTSUMI, Masafumi y Takeshi CHISHAKI. "A study on time-series prediction system and AROP model of nonstationary-type process for transportation demand." Doboku Gakkai Ronbunshu, n.º 449 (1992): 125–33. http://dx.doi.org/10.2208/jscej.1992.449_125.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

43

Shang, X., Y. Zhang, G. Zhang, X. Chai, A. Deng, Y. Liang y T. Wen. "Characterization and Molecular Mechanism of AroP as an Aromatic Amino Acid and Histidine Transporter in Corynebacterium glutamicum". Journal of Bacteriology 195, n.º 23 (20 de septiembre de 2013): 5334–42. http://dx.doi.org/10.1128/jb.00971-13.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

44

Duncan, K., R. M. Edwards y J. R. Coggins. "The pentafunctional arom enzyme of Saccharomyces cerevisiae is a mosaic of monofunctional domains". Biochemical Journal 246, n.º 2 (1 de septiembre de 1987): 375–86. http://dx.doi.org/10.1042/bj2460375.

Texto completo

Resumen

The nucleotide sequence of the Saccharomyces cerevisiae ARO1 gene which encodes the arom multifunctional enzyme has been determined. The protein sequence deduced for the pentafunctional arom polypeptide is 1588 amino acids in length and has a calculated Mr of 174555. Functional regions within the polypeptide chain have been identified by comparison with the sequences of the five monofunctional Escherichia coli enzymes whose activities correspond with those of the arom multifunctional enzyme. The observed homologies demonstrate that the arom polypeptide is a mosaic of functional domains and are consistent with the hypothesis that the ARO1 gene evolved by the linking of ancestral E. coli-like genes.

Los estilos APA, Harvard, Vancouver, ISO, etc.

45

Khalil, Ali, Saad Saba, Catherine Ribault, Manuel Vlach, Pascal Loyer, Olivier Coulembier y Sandrine Cammas-Marion. "Synthesis of Poly(Dimethylmalic Acid) Homo- and Copolymers to Produce Biodegradable Nanoparticles for Drug Delivery: Cell Uptake and Biocompatibility Evaluation in Human Heparg Hepatoma Cells". Polymers 12, n.º 8 (29 de julio de 2020): 1705. http://dx.doi.org/10.3390/polym12081705.

Texto completo

Resumen

Hydrophobic and amphiphilic derivatives of the biocompatible and biodegradable poly(dimethylmalic acid) (PdiMeMLA), varying by the nature of the lateral chains and the length of each block, respectively, have been synthesized by anionic ring-opening polymerization (aROP) of the corresponding monomers using an initiator/base system, which allowed for very good control over the (co)polymers’ characteristics (molar masses, dispersity, nature of end-chains). Hydrophobic and core-shell nanoparticles (NPs) were then prepared by nanoprecipitation of hydrophobic homopolymers and amphiphilic block copolymers, respectively. Negatively charged NPs, showing hydrodynamic diameters (Dh) between 50 and 130 nm and narrow size distributions (0.08 < PDI < 0.22) depending on the (co)polymers nature, were obtained and characterized by dynamic light scattering (DLS), zetametry, and transmission electron microscopy (TEM). Finally, the cytotoxicity and cellular uptake of the obtained NPs were evaluated in vitro using the hepatoma HepaRG cell line. Our results showed that both cytotoxicity and cellular uptake were influenced by the nature of the (co)polymer constituting the NPs.

Los estilos APA, Harvard, Vancouver, ISO, etc.

46

Ghosh, Suman, Bessie W. Kebaara, Audrey L. Atkin y Kenneth W. Nickerson. "Regulation of Aromatic Alcohol Production in Candida albicans". Applied and Environmental Microbiology 74, n.º 23 (3 de octubre de 2008): 7211–18. http://dx.doi.org/10.1128/aem.01614-08.

Texto completo

Resumen

ABSTRACT Colonization by the fungal pathogen Candida albicans varies significantly, depending upon the pH and availability of oxygen. Because of our interest in extracellular molecules as potential quorum-sensing molecules, we examined the physiological conditions which regulate the production of the aromatic alcohols, i.e., phenethyl alcohol, tyrosol, and tryptophol. The production of these fusel oils has been well studied for Saccharomyces cerevisiae. Our data show that aromatic alcohol yields for C. albicans are determined by growth conditions. These conditions include the availability of aromatic amino acids, the pH, oxygen levels, and the presence of ammonium salts. For example, for wild-type C. albicans, tyrosol production varied 16-fold merely with the inclusion of tyrosine or ammonium salts in the growth medium. Aromatic alcohol production also depends on the transcription regulator Aro80p. Our results are consistent with aromatic alcohol production—aromatic transaminases (gene products for ARO8 and ARO9), aromatic decarboxylase (ARO10), and alcohol dehydrogenase (ADH)—via the fusel oil pathway. The expression of ARO8, ARO9, and ARO10 is also pH dependent. ARO8 and ARO9 were alkaline upregulated, while ARO10 was alkaline downregulated. The alkaline-dependent change in expression of ARO8 was Rim101 independent, while the expression of ARO9 was Rim101 dependent.

Los estilos APA, Harvard, Vancouver, ISO, etc.

47

Domiński, Adrian, Tomasz Konieczny, Magdalena Zięba, Magdalena Klim y Piotr Kurcok. "Anionic Polymerization of β-Butyrolactone Initiated with Sodium Phenoxides. The Effect of the Initiator Basicity/Nucleophilicity on the ROP Mechanism". Polymers 11, n.º 7 (22 de julio de 2019): 1221. http://dx.doi.org/10.3390/polym11071221.

Texto completo

Resumen

It was shown that selected sodium phenoxide derivatives with different basicity and nucleophilicity, such as sodium p-nitrophenoxide, p-chlorophenoxide, 1-napthoxide, phenoxide and p-methoxyphenoxide, are effective initiators in anionic ring-opening polymerization (AROP) of β-butyrolactone in mild conditions. It was found that phenoxides as initiators in anionic ring-opening polymerization of β-butyrolactone behave as strong nucleophiles, or weak nucleophiles, as well as Brønsted bases. The resulting polyesters possessing hydroxy, phenoxy and crotonate initial groups are formed respectively by the attack of phenoxide anion at (i) C2 followed by an elimination reaction with hydroxide formation, (ii) C4 and (iii) abstraction of acidic proton at C3. The obtained poly(3-hydroxybutyrate) possesses carboxylate growing species. The ratio of the observed initial groups strongly depends on the basicity and nucleophilicity of the sodium phenoxide derivative used as initiator. The proposed mechanism of this polymerization describes the reactions leading to formation of observed end groups. Moreover, the possibility of formation of a crotonate group during the propagation step of this polymerization is also discussed.

Los estilos APA, Harvard, Vancouver, ISO, etc.

48

Bacher, Jamie M. y Andrew D. Ellington. "Selection and Characterization of Escherichia coliVariants Capable of Growth on an Otherwise Toxic Tryptophan Analogue". Journal of Bacteriology 183, n.º 18 (15 de septiembre de 2001): 5414–25. http://dx.doi.org/10.1128/jb.183.18.5414-5425.2001.

Texto completo

Resumen

ABSTRACT Escherichia coli isolates that were tolerant of incorporation of high proportions of 4-fluorotryptophan were evolved by serial growth. The resultant strain still preferred tryptophan for growth but showed improved growth relative to the parental strain on other tryptophan analogues. Evolved clones fully substituted fluorotryptophan for tryptophan in their proteomes within the limits of mass spectral and amino acid analyses. Of the genes sequenced, many genes were found to be unaltered in the evolved strain; however, three genes encoding enzymes involved in tryptophan uptake and utilization were altered: the aromatic amino acid permease (aroP) and tryptophanyl-tRNA synthetase (trpS) contained several amino acid substitutions, and the tyrosine repressor (tyrR) had a nonsense mutation. While kinetic analysis of the tryptophanyl-tRNA synthetase suggests discrimination against 4-fluorotryptophan, an analysis of the incorporation and growth patterns of the evolved bacteria suggest that other mutations also aid in the adaptation to the tryptophan analogue. These results suggest that the incorporation of unnatural amino acids into organismal proteomes may be possible but that extensive evolution may be required to reoptimize proteins and metabolism to accommodate such analogues.

Los estilos APA, Harvard, Vancouver, ISO, etc.

49

Chen, ST, JD Lin y KH Lin. "Characterization of a thyroid hormone-mediated short-loop feedback control of TSH receptor gene in an anaplastic human thyroid cancer cell line". Journal of Endocrinology 175, n.º 2 (1 de noviembre de 2002): 459–65. http://dx.doi.org/10.1677/joe.0.1750459.

Texto completo

Resumen

The expression of TSH receptor (TSHR) gene is frequently lost in thyroid cancers during the process of dedifferentiation that involves perturbation of several nuclear transcription factors. We have established that thyroid hormone receptor beta1 (TRbeta1) is associated with the loss of TSHR gene expression in an anaplastic human thyroid cancer cell line, ARO. To demonstrate that TRbeta1 regulates TSHR gene expression, we performed electrophoresis mobility shift and 3,5,3'-triiodothyronine (T3) transactivation assays. As expected, TRbeta1 bound the synthesized oligomer containing TSHR promoter sequence by heterodimerizing with retinoid X receptor. When a chimeric reporter pTRCAT5'-146 enclosing the minimal TSHR promoter was applied for T3 transactivation assay, two TRbeta1-overexpressing transfectants of ARO cells (ARO1 and ARO2) demonstrated higher basal activity than their parental cells. Consequentially, T3 suppressed the reporter gene activity only in ARO1 and ARO2, but not in ARO cells. A point mutation creating a cAMP response element (CRE) in the reporter pTRCAT5'-146 CRE led to T3-induced suppression of the reporter gene in ARO cells without changing the basal or T3-induced activities in ARO1 and ARO2 cells. We conclude that the regulatory effect of T3 on TSHR gene expression is TR- and promoter DNA sequence-determined.

Los estilos APA, Harvard, Vancouver, ISO, etc.

50

Fawzy, Wafaa M. y M. C. Heaven. "Electronic spectroscopy of the ArOH and ArOD complexes". Journal of Chemical Physics 92, n.º 2 (15 de enero de 1990): 909–16. http://dx.doi.org/10.1063/1.458125.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

Artículos de revistas sobre el tema "AROP"

Crea una cita precisa en los estilos APA, MLA, Chicago, Harvard y otros