Accedi

Bibliografie tematiche / Urea / Articoli di riviste

Segui questo link per vedere altri tipi di pubblicazioni sul tema: Urea.

Articoli di riviste sul tema "Urea"

Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 29 luglio 2024

Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili

Scegli il tipo di fonte:

Vedi i top-50 articoli di riviste per l'attività di ricerca sul tema "Urea".

Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.

Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.

Vedi gli articoli di riviste di molte aree scientifiche e compila una bibliografia corretta.

1

Heimer, Susan R., e Harry L. T. Mobley. "Interaction of Proteus mirabilis Urease Apoenzyme and Accessory Proteins Identified with Yeast Two-Hybrid Technology". Journal of Bacteriology 183, n. 4 (15 febbraio 2001): 1423–33. http://dx.doi.org/10.1128/jb.183.4.1423-1433.2001.

Testo completo

Abstract (sommario):

ABSTRACT Proteus mirabilis, a gram-negative bacterium associated with complicated urinary tract infections, produces a metalloenzyme urease which hydrolyzes urea to ammonia and carbon dioxide. The apourease is comprised of three structural subunits, UreA, UreB, and UreC, assembled as a homotrimer of individual UreABC heterotrimers (UreABC)3. To become catalytically active, apourease acquires divalent nickel ions through a poorly understood process involving four accessory proteins, UreD, UreE, UreF, and UreG. While homologues of UreD, UreF, and UreG have been copurified with apourease, it remains unclear specifically how these polypeptides associate with the apourease or each other. To identify interactions among P. mirabilis accessory proteins, in vitro immunoprecipitation and in vivo yeast two-hybrid assays were employed. A complex containing accessory protein UreD and structural protein UreC was isolated by immunoprecipitation and characterized with immunoblots. This association occurs independently of coaccessory proteins UreE, UreF, and UreG and structural protein UreA. In a yeast two-hybrid screen, UreD was found to directly interact in vivo with coaccessory protein UreF. Unique homomultimeric interactions of UreD and UreF were also detected in vivo. To substantiate the study of urease proteins with a yeast two-hybrid assay, previously described UreE dimers and homomultimeric UreA interactions among apourease trimers were confirmed in vivo. Similarly, a known structural interaction involving UreA and UreC was also verified. This report suggests that in vivo, P. mirabilis UreD may be important for recruitment of UreF to the apourease and that crucial homomultimeric associations occur among these accessory proteins.

Gli stili APA, Harvard, Vancouver, ISO e altri

2

Voland, Petra, David L. Weeks, Elizabeth A. Marcus, Christian Prinz, George Sachs e David Scott. "Interactions among the sevenHelicobacter pyloriproteins encoded by the urease gene cluster". American Journal of Physiology-Gastrointestinal and Liver Physiology 284, n. 1 (1 gennaio 2003): G96—G106. http://dx.doi.org/10.1152/ajpgi.00160.2002.

Testo completo

Abstract (sommario):

Survival of Helicobacter pylori in acid depends on intrabacterial urease. This urease is a Ni2+-containing oligomeric heterodimer. Regulation of its activity and assembly is important for gastric habitation by this neutralophile. The gene complex encodes catalytic subunits ( ureA/B), an acid-gated urea channel ( ureI), and accessory assembly proteins ( ureE–H). With the use of yeast two-hybrid analysis for determining protein-protein interactions, UreF as bait identified four interacting sequences encoding UreH, whereas UreG as bait detected five UreE sequences. These results were confirmed by coimmunoprecipitation and β-galactosidase assays. Native PAGE immunoblotting of H. pylori inner membranes showed interaction of UreA/B with UreI, whereas UreI deletion mutants lacked this protein interaction. Deletion of ureE–H did not affect this interaction with UreI. Hence, the accessory proteins UreE/G and UreF/H form dimeric complexes and UreA/B form a membrane complex with UreI, perhaps enabling assembly of the urease apoenzyme at the membrane surface and immediate urea access to intrabacterial urease to allow rapid periplasmic neutralization.

Gli stili APA, Harvard, Vancouver, ISO e altri

3

Sangari, Félix J., Asunción Seoane, María Cruz Rodríguez, Jesús Agüero e Juan M. García Lobo. "Characterization of the Urease Operon of Brucella abortus and Assessment of Its Role in Virulence of the Bacterium". Infection and Immunity 75, n. 2 (13 novembre 2006): 774–80. http://dx.doi.org/10.1128/iai.01244-06.

Testo completo

Abstract (sommario):

ABSTRACT Most members of the genus Brucella show strong urease activity. However, the role of this enzyme in the pathogenesis of Brucella infections is poorly understood. We isolated several Tn5 insertion mutants deficient in urease activity from Brucella abortus strain 2308. The mutations of most of these mutants mapped to a 5.7-kbp DNA region essential for urease activity. Sequencing of this region, designated ure1, revealed the presence of seven open reading frames corresponding to the urease structural proteins (UreA, UreB, and UreC) and the accessory proteins (UreD, UreE, UreF, and UreG). In addition to the urease genes, another gene (cobT) was identified, and inactivation of this gene affected urease activity in Brucella. Subsequent analysis of the previously described sequences of the genomes of Brucella spp. revealed the presence of a second urease cluster, ure2, in all them. The ure2 locus was apparently inactive in B. abortus 2308. Urease-deficient mutants were used to evaluate the role of urease in Brucella pathogenesis. The urease-producing strains were found to be resistant in vitro to strong acid conditions in the presence of urea, while urease-negative mutants were susceptible to acid treatment. Similarly, the urease-negative mutants were killed more efficiently than the urease-producing strains during transit through the stomach. These results suggested that urease protects brucellae during their passage through the stomach when the bacteria are acquired by the oral route, which is the major route of infection in human brucellosis.

Gli stili APA, Harvard, Vancouver, ISO e altri

4

Yuen, Man Hon, Yu Hang Fong, Yap Shing Nim, Pak Ho Lau e Kam-Bo Wong. "Structural insights into how GTP-dependent conformational changes in a metallochaperone UreG facilitate urease maturation". Proceedings of the National Academy of Sciences 114, n. 51 (4 dicembre 2017): E10890—E10898. http://dx.doi.org/10.1073/pnas.1712658114.

Testo completo

Abstract (sommario):

The ability of metallochaperones to allosterically regulate the binding/release of metal ions and to switch protein-binding partners along the metal delivery pathway is essential to the metallation of the metalloenzymes. Urease, catalyzing the hydrolysis of urea into ammonia and carbon dioxide, contains two nickel ions bound by a carbamylated lysine in its active site. Delivery of nickel ions for urease maturation is dependent on GTP hydrolysis and is assisted by four urease accessory proteins UreE, UreF, UreG, and UreH(UreD). Here, we determined the crystal structure of the UreG dimer from Klebsiella pneumoniae in complex with nickel and GMPPNP, a nonhydrolyzable analog of GTP. Comparison with the structure of the GDP-bound Helicobacter pylori UreG (HpUreG) in the UreG2F2H2 complex reveals large conformational changes in the G2 region and residues near the 66CPH68 metal-binding motif. Upon GTP binding, the side chains of Cys66 and His68 from each of the UreG protomers rotate toward each other to coordinate a nickel ion in a square-planar geometry. Mutagenesis studies on HpUreG support the conformational changes induced by GTP binding as essential to dimerization of UreG, GTPase activity, in vitro urease activation, and the switching of UreG from the UreG2F2H2 complex to form the UreE2G2 complex with the UreE dimer. The nickel-charged UreE dimer, providing the sole source of nickel, and the UreG2F2H2 complex could activate urease in vitro in the presence of GTP. Based on our results, we propose a mechanism of how conformational changes of UreG during the GTP hydrolysis/binding cycle facilitate urease maturation.

Gli stili APA, Harvard, Vancouver, ISO e altri

5

Scott, David R., Elizabeth A. Marcus, Yi Wen, Siddarth Singh, Jing Feng e George Sachs. "Cytoplasmic Histidine Kinase (HP0244)-Regulated Assembly of Urease with UreI, a Channel for Urea and Its Metabolites, CO2, NH3, and NH4+, Is Necessary for Acid Survival of Helicobacter pylori". Journal of Bacteriology 192, n. 1 (23 ottobre 2009): 94–103. http://dx.doi.org/10.1128/jb.00848-09.

Testo completo

Abstract (sommario):

ABSTRACT Helicobacter pylori colonizes the normal human stomach by maintaining both periplasmic and cytoplasmic pH close to neutral in the presence of gastric acidity. Urease activity, urea flux through the pH-gated urea channel, UreI, and periplasmic α-carbonic anhydrase are essential for colonization. Exposure to pH 4.5 for up to 180 min activates total bacterial urease threefold. Within 30 min at pH 4.5, the urease structural subunits, UreA and UreB, and the Ni2+ insertion protein, UreE, are recruited to UreI at the inner membrane. Formation of this complex and urease activation depend on expression of the cytoplasmic sensor histidine kinase, HP0244. Its deletion abolishes urease activation and assembly, impairs cytoplasmic and periplasmic pH homeostasis, and depolarizes the cells, with an ∼7-log loss of survival at pH 2.5, even in 10 mM urea. Associated with this assembly, UreI is able to transport NH3, NH4 +, and CO2, as shown by changes in cytoplasmic pH following exposure to NH4Cl or CO2. To be able to colonize cells in the presence of the highly variable pH of the stomach, the organism expresses two pH-sensor histidine kinases, one, HP0165, responding to a moderate fall in periplasmic pH and the other, HP0244, responding to cytoplasmic acidification at a more acidic medium pH. Assembly of a pH-regulatory complex of active urease with UreI provides an advantage for periplasmic buffering.

Gli stili APA, Harvard, Vancouver, ISO e altri

6

Kasatkina, Svetlana O., Kirill K. Geyl, Sergey V. Baykov, Mikhail S. Novikov e Vadim P. Boyarskiy. "“Urea to Urea” Approach: Access to Unsymmetrical Ureas Bearing Pyridyl Substituents". Advanced Synthesis & Catalysis 364, n. 7 (8 marzo 2022): 1295–304. http://dx.doi.org/10.1002/adsc.202101490.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

7

Masepohl, Bernd, Björn Kaiser, Nazila Isakovic, Cynthia L. Richard, Robert G. Kranz e Werner Klipp. "Urea Utilization in the Phototrophic BacteriumRhodobacter capsulatus Is Regulated by the Transcriptional Activator NtrC". Journal of Bacteriology 183, n. 2 (15 gennaio 2001): 637–43. http://dx.doi.org/10.1128/jb.183.2.637-643.2001.

Testo completo

Abstract (sommario):

ABSTRACT The phototrophic nonsulfur purple bacteriumRhodobacter capsulatus can use urea as a sole source of nitrogen. Three transposon Tn5-induced mutations (Xan-9, Xan-10, and Xan-19), which led to a Ure−phenotype, were mapped to the ureF and ureCgenes, whereas two other Tn5 insertions (Xan-20 and Xan-22) were located within the ntrC and ntrB genes, respectively. As in Klebsiella aerogenes and other bacteria, the genes encoding urease (ureABC) and the genes required for assembly of the nickel metallocenter (ureD andureEFG) are clustered in R. capsulatus(ureDABC-orf136-ureEFG). No homologues of Orf136 were found in the databases, and mutational analysis demonstrated that orf136 is not essential for urease activity or growth on urea. Analysis of aureDA-lacZ fusion showed that maximum expression of the ure genes occurred under nitrogen-limiting conditions (e.g., serine or urea as the sole nitrogen source), but ure gene expression was not substrate (urea) inducible. Expression of the ure genes was strictly dependent on NtrC, whereas ς54 was not essential for urease activity. Expression of the ure genes was lower (by a factor of 3.5) in the presence of ammonium than under nitrogen-limiting conditions, but significant transcription was also observed in the presence of ammonium, approximately 10-fold higher than in an ntrC mutant background. Thus, ure gene expression in the presence of ammonium also requires NtrC. Footprint analyses demonstrated binding of NtrC to tandem binding sites upstream of the ureD promoter. Phosphorylation of NtrC increased DNA binding by at least eightfold. Although urea is effectively used as a nitrogen source in an NtrC-dependent manner, nitrogenase activity was not repressed by urea.

Gli stili APA, Harvard, Vancouver, ISO e altri

8

Wen, Yi, Jing Feng, David R. Scott, Elizabeth A. Marcus e George Sachs. "The pH-Responsive Regulon of HP0244 (FlgS), the Cytoplasmic Histidine Kinase of Helicobacter pylori". Journal of Bacteriology 191, n. 2 (31 ottobre 2008): 449–60. http://dx.doi.org/10.1128/jb.01219-08.

Testo completo

Abstract (sommario):

ABSTRACT Helicobacter pylori colonizes the acidic gastric environment, in contrast to all other neutralophiles, whose acid resistance and tolerance responses allow only gastric transit. This acid adaptation is dependent on regulation of gene expression in response to pH changes in the periplasm and cytoplasm. The cytoplasmic histidine kinase, HP0244, which until now was thought only to regulate flagellar gene expression via its cognate response regulator, HP0703, was found to generate a response to declining medium pH. Although not required for survival at pH 4.5, HP0244 is required for survival at pH 2.5 with 10 mM urea after 30 min. Transcriptional profiling of a HP0244 deletion mutant grown at pH 7.4 confirmed the contribution of HP0244 to σ54 activation via HP0703 to coordinate flagellar biosynthesis by a pH-independent regulon that includes 14 flagellar genes. Microarray analysis of cells grown at pH 4.5 without urea revealed an additional 22 genes, including 4 acid acclimation genes (ureA, ureB, ureI, and amiE) that are positively regulated by HP0244. Additionally, 86 differentially expressed genes, including 3 acid acclimation genes (ureF, rocF [arginase], and ansB [asparaginase]), were found in cells grown at pH 2.5 with 30 mM urea. Hence, HP0244 has, in addition to the pH-independent flagellar regulon, a pH-dependent regulon, which allows adaptation to a wider range of environmental acid conditions. An acid survival study using an HP0703 mutant and an electrophoretic mobility shift assay with in vitro-phosphorylated HP0703 showed that HP0703 does not contribute to acid survival and does not bind to the promoter regions of several genes in the HP0244 pH-dependent regulon, suggesting that there is a pathway outside the HP0703 regulon which transduces the acid-responsive signal sensed by HP0244.

Gli stili APA, Harvard, Vancouver, ISO e altri

9

Abdulrahman, Alia Talaat, Shna Ibrahim Ismail, Salar Saadi Hussain, Najat Jabbar Ahmed e Ahmed Nawzad Hassan. "Detection of Helicobacter Pylori’s Virulence Gene (UreA) and its Influence on the Result of Rapid Urease Test (RUT)". Al-Mustansiriyah Journal of Science 33, n. 4 (30 dicembre 2022): 42–48. http://dx.doi.org/10.23851/mjs.v33i4.1152.

Testo completo

Abstract (sommario):

UreA is an important virulence factor of Helicobacter pylori that, along with UreB and UreC, produces urease. Urease enzyme helps the bacterium to colonize the human stomach through metabolizing urea in order to neutralize the gastric environment. The current study aimed to detect the prevalence of the H. pylori’s ureA virulence factor gene, and to investigate the influence of this gene on the result of the rapid urease test (RUT). Eighty stomach biopsy samples were isolated from participants who were suspected to be infected with H. pylori in Erbil city. Participants were 36 males and 44 females, aged between 18 and 67 years. The results showed that 42 (52.5%) of the participants were positive for H. pylori when tested by RUT, while 59 (73.8%) of the patients showed positive H. pylori infection when tested by polymerase chain reaction (PCR) targeting the 16S rRNA gene. The results of the PCR test based on the ureA gene revealed that 42 (52.5%) of the samples were positive. The important finding of this research is the presence of 100% compatibility between positive samples of RUT and ureA genes. It can be concluded from this study that a person may be infected with H. pylori, but the RUT test fails to detect the infection if the bacteria lack the ureA gene, indicating a direct impact of this gene on the result of RUT, which is a defect of RUT.

Gli stili APA, Harvard, Vancouver, ISO e altri

10

Scott, David R., Elizabeth A. Marcus, David L. Weeks, Adrian Lee, Klaus Melchers e George Sachs. "Expression of the Helicobacter pylori ureI Gene Is Required for Acidic pH Activation of Cytoplasmic Urease". Infection and Immunity 68, n. 2 (1 febbraio 2000): 470–77. http://dx.doi.org/10.1128/iai.68.2.470-477.2000.

Testo completo

Abstract (sommario):

ABSTRACT ureI encodes an integral cytoplasmic membrane protein. It is present in the urease gene cluster of Helicobacter pylori and is essential for infection and acid survival, but its role is unknown. To determine the function of UreI protein, we producedH. pylori ureI deletion mutants and measured the pH dependence of urease activity of intact and lysed bacteria and the effect of urea on the membrane potential. We also determinedureI expression, urease activity, and the effect of urea on membrane potential of several gastric and nongastricHelicobacter species. ureI was found to be present in the genome of the gastric Helicobacter species and absent in the nongastric Helicobacter species studied, as determined by PCR. Likewise, Western blot analysis confirmed that UreI was expressed only in the gastric Helicobacterspecies. When UreI is present, acidic medium pH activation of cytoplasmic urease is found, and urea addition increases membrane potential at acidic pH. The addition of a low concentration of detergent raised urease activity of intact bacteria at neutral pH to that of their homogenates, showing that urease activity was membrane limited. No acidic pH activation or urea induced membrane potential changes were found in the nongastric Helicobacter species. The ureI gene product is probably a pH activated urea transporter or perhaps regulates such a transporter as a function of periplasmic pH.

Gli stili APA, Harvard, Vancouver, ISO e altri

11

Janovec, Ladislav, Eva Kovacova, Martina Semelakova, Monika Kvakova, Daniel Kupka, David Jager e Maria Kozurkova. "Synthesis of Novel Biologically Active Proflavine Ureas Designed on the Basis of Predicted Entropy Changes". Molecules 26, n. 16 (11 agosto 2021): 4860. http://dx.doi.org/10.3390/molecules26164860.

Testo completo

Abstract (sommario):

A novel series of proflavine ureas, derivatives 11a–11i, were synthesized on the basis of molecular modeling design studies. The structure of the novel ureas was obtained from the pharmacological model, the parameters of which were determined from studies of the structure-activity relationship of previously prepared proflavine ureas bearing n-alkyl chains. The lipophilicity (LogP) and the changes in the standard entropy (ΔS°) of the urea models, the input parameters of the pharmacological model, were determined using quantum mechanics and cheminformatics. The anticancer activity of the synthesized derivatives was evaluated against NCI-60 human cancer cell lines. The urea derivatives azepyl 11b, phenyl 11c and phenylethyl 11f displayed the highest levels of anticancer activity, although the results were only a slight improvement over the hexyl urea, derivative 11j, which was reported in a previous publication. Several of the novel urea derivatives displayed GI50 values against the HCT-116 cancer cell line, which suggest the cytostatic effect of the compounds azepyl 11b–0.44 μM, phenyl 11c–0.23 μM, phenylethyl 11f–0.35 μM and hexyl 11j–0.36 μM. In contrast, the novel urea derivatives 11b, 11c and 11f exhibited levels of cytotoxicity three orders of magnitude lower than that of hexyl urea 11j or amsacrine.

Gli stili APA, Harvard, Vancouver, ISO e altri

12

Kim, Jong Kyong, Scott B. Mulrooney e Robert P. Hausinger. "The UreEF Fusion Protein Provides a Soluble and Functional Form of the UreF Urease Accessory Protein". Journal of Bacteriology 188, n. 24 (13 ottobre 2006): 8413–20. http://dx.doi.org/10.1128/jb.01265-06.

Testo completo

Abstract (sommario):

ABSTRACT Four accessory proteins (UreD, UreE, UreF, and UreG) are typically required to form the nickel-containing active site in the urease apoprotein (UreABC). Among the accessory proteins, UreD and UreF have been elusive targets for biochemical and structural characterization because they are not overproduced as soluble proteins. Using the best-studied urease system, in which the Klebsiella aerogenes genes are expressed in Escherichia coli, a translational fusion of ureE and ureF was generated. The UreEF fusion protein was overproduced as a soluble protein with a convenient tag involving the His-rich region of UreE. The fusion protein was able to form a UreD(EF)G-UreABC complex and to activate urease in vivo, and it interacted with UreD-UreABC in vitro to form a UreD(EF)-UreABC complex. While the UreF portion of UreEF is fully functional, the fusion significantly affected the role of the UreE portion by interrupting its dimerization and altering its metal binding properties compared to those of the wild-type UreE. Analysis of a series of UreEF deletion mutants revealed that the C terminus of UreF is required to form the UreD(EF)G-UreABC complex, while the N terminus of UreF is essential for activation of urease.

Gli stili APA, Harvard, Vancouver, ISO e altri

13

Saro, Mateo, Andrés, Mateos, Ranilla, López, Martín e Giráldez. "Replacing Soybean Meal with Urea in Diets for Heavy Fattening Lambs: Effects on Growth, Metabolic Profile and Meat Quality". Animals 9, n. 11 (14 novembre 2019): 974. http://dx.doi.org/10.3390/ani9110974.

Testo completo

Abstract (sommario):

Thirty-six Assaf male lambs (29.4 ± 3.10 kg body weight (BW)) were used to study the feasibility of including urea (at 0, 0.6 or 0.95% of dry matter for Control, Urea1, and Urea2 diets, respectively) in substitution of soybean meal in fattening diets. Animals were individually penned and feed intake was recorded daily. Blood samples were taken at days 35 and 63 of the experimental period to determine the acid-base status and the biochemical profile. At the end of the experiment (nine weeks), lambs were slaughtered, ruminal contents were collected and carcass and meat quality were evaluated. There were not differences (p > 0.05) among treatments in dry matter intake, animal performance, ruminal fermentation pattern, and carcass and meat parameters. Serum albumin concentration was higher and concentration of HCO3 and total CO2 in blood were lower in Urea2 compared to Urea1 and Control lambs. These results, together with the tendency to lower (p = 0.065) blood pH in this group might suggest a moderate metabolic acidosis. Partial replacement of soybean meal with urea did not impair growth rate in heavy fattening Assaf lambs (from 29 to 50 kg body weight), reduced feeding costs and had no adverse effects on feed efficiency, rumen fermentation and carcass and meat quality.

Gli stili APA, Harvard, Vancouver, ISO e altri

14

Spencer, J. N., e James W. Hovick. "Solvation of urea and methyl-substituted ureas by water and DMF". Canadian Journal of Chemistry 66, n. 4 (1 aprile 1988): 562–65. http://dx.doi.org/10.1139/v88-096.

Testo completo

Abstract (sommario):

The hydrogen bond enthalpies of urea and methyl-substituted ureas with water and DMF have been determined by the pure-base calorimetric method. Transfer enthalpies between water and DMF have been calculated for dilute solutions of the ureas according to a previously developed model. The first solvation sphere of urea in water consists of five water molecules. Solvation spheres are given for other methyl-substituted ureas in water and DMF.

Gli stili APA, Harvard, Vancouver, ISO e altri

15

Varma, Ashok, Shaoxi Wu, Ningru Guo, Wanqing Liao, Guxia Lu, Anshen Li, Yonglin Hu, Glenn Bulmer e Kyung J. Kwon-Chung. "Identification of a novel gene, URE2, that functionally complements a urease-negative clinical strain of Cryptococcus neoformans". Microbiology 152, n. 12 (1 dicembre 2006): 3723–31. http://dx.doi.org/10.1099/mic.0.2006/000133-0.

Testo completo

Abstract (sommario):

A urease-negative serotype A strain of Cryptococcus neoformans (B-4587) was isolated from the cerebrospinal fluid of an immunocompetent patient with a central nervous system infection. The URE1 gene encoding urease failed to complement the mutant phenotype. Urease-positive clones of B-4587 obtained by complementing with a genomic library of strain H99 harboured an episomal plasmid containing DNA inserts with homology to the sudA gene of Aspergillus nidulans. The gene harboured by these plasmids was named URE2 since it enabled the transformants to grow on media containing urea as the sole nitrogen source while the transformants with an empty vector failed to grow. Transformation of strain B-4587 with a plasmid construct containing a truncated version of the URE2 gene failed to complement the urease-negative phenotype. Disruption of the native URE2 gene in a wild-type serotype A strain H99 and a serotype D strain LP1 of C. neoformans resulted in the inability of the strains to grow on media containing urea as the sole nitrogen source, suggesting that the URE2 gene product is involved in the utilization of urea by the organism. Virulence in mice of the urease-negative isolate B-4587, the urease-positive transformants containing the wild-type copy of the URE2 gene, and the urease-negative vector-only transformants was comparable to that of the H99 strain of C. neoformans regardless of the infection route. Virulence of the URE2 disruption stain of H99 was slightly reduced compared to the wild-type strain in the intravenous model but was significantly attenuated in the inhalation model. These results indicate that the importance of urease activity in pathogenicity varies depending on the strains of C. neoformans used and/or the route of infection. Furthermore, this study shows that complementation cloning can serve as a useful tool to functionally identify genes such as URE2 that have otherwise been annotated as hypothetical proteins in genomic databases.

Gli stili APA, Harvard, Vancouver, ISO e altri

16

P, PARAMASIVAM. "COMPARATIVE MINERALISATION EFFECT OF SLOW RELEASE FERTILIZERS IN SOILS OF CHOLAVANDAN BASIN TRACT - TAMIL NADU". Madras Agricultural Journal 78, March Augest (1991): 156–60. http://dx.doi.org/10.29321/maj.10.a01832.

Testo completo

Abstract (sommario):

The comparative mineralisation effect of Urea formaldehyde (UF), Tarcoated urea (TCU) and Lac coated urea (LCU) was studied in the predominant soll series of Cholavantin basin tract of Tamil Nadu under two moisture regimes. The results showed that after 4 days of Incubation, the amount of urea was the lowest in the treatment receiving urea in all the soils and the two moisture regimes. The amount of urea released from LCU and TCU Immediately after application in solls was quite high. The rate of release of urea-N from UF was the highest In all the soll series. The amount of NHLAN found in solls treated with different fertilizers was In the order Uren TCU LCU UF. The conversion of NII4 to NO2 and NOy form with urea was rapid in the case of Padugal and Analyur series particularly in 75% WHC moisture regime. The rate of decomposition of all the fertilizers is more in Palaviduthi series, whereas in padugal and Analyur series It is slow and incomplete.

Gli stili APA, Harvard, Vancouver, ISO e altri

17

Koper, Teresa E., Amal F. El-Sheikh, Jeanette M. Norton e Martin G. Klotz. "Urease-Encoding Genes in Ammonia-Oxidizing Bacteria". Applied and Environmental Microbiology 70, n. 4 (aprile 2004): 2342–48. http://dx.doi.org/10.1128/aem.70.4.2342-2348.2004.

Testo completo

Abstract (sommario):

ABSTRACT Many but not all ammonia-oxidizing bacteria (AOB) produce urease (urea amidohydrolase, EC 3.5.1.5) and are capable of using urea for chemolithotrophic growth. We sequenced the urease operons from two AOB, the β-proteobacterium Nitrosospira sp. strain NpAV and the γ-proteobacterium Nitrosococcus oceani. In both organisms, all seven urease genes were contiguous: the three structural urease genes ureABC were preceded and succeeded by the accessory genes ureD and ureEFG, respectively. Green fluorescent protein reporter gene fusions revealed that the ure genes were under control of a single operon promoter upstream of the ureD gene in Nitrosococcus oceani. Southern analyses revealed two copies of ureC in the Nitrosospira sp. strain NpAV genome, while a single copy of the ure operon was detected in the genome of Nitrosococcus oceani. The ureC gene encodes the alpha subunit protein containing the active site and conserved nickel binding ligands; these conserved regions were suitable primer targets for obtaining further ureC sequences from additional AOB. In order to develop molecular tools for detecting the ureolytic ecotype of AOB, ureC genes were sequenced from several β-proteobacterial AOB. Pairwise identity values ranged from 80 to 90% for the UreC peptides of AOB within a subdivision. UreC sequences deduced from AOB urease genes and available UreC sequences in the public databases were used to construct alignments and make phylogenetic inferences. The UreC proteins from β-proteobacterial AOB formed a distinct monophyletic group. Unexpectedly, the peptides from AOB did not group most closely with the UreC proteins from other β-proteobacteria. Instead, it appears that urease in β-proteobacterial autotrophic ammonia oxidizers is the product of divergent evolution in the common ancestor of γ- and β-proteobacteria that was initiated before their divergence during speciation. Sequence motifs conserved for the proteobacteria and variable regions possibly discriminatory for ureC from β-proteobacterial AOB were identified for future use in environmental analysis of ureolytic AOB. These gene sequences are the first publicly available for ure genes from autotrophic AOB.

Gli stili APA, Harvard, Vancouver, ISO e altri

18

&NA;. "Urea". Reactions Weekly &NA;, n. 1405 (giugno 2012): 37. http://dx.doi.org/10.2165/00128415-201214050-00129.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

19

Young, Jay A. "Urea". Journal of Chemical Education 84, n. 9 (settembre 2007): 1421. http://dx.doi.org/10.1021/ed084p1421.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

20

Maduell, F., J. Garcia-Valdecasas, H. Garcia, J. Hdez-Jaras, F. Sigüenza, C. del Pozo, R. Giner, R. Moll e E. Garrigos. "Urea Reduction Ratio Considering Urea Rebound". Nephron 78, n. 2 (1998): 143–47. http://dx.doi.org/10.1159/000044902.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

21

Nim, Yap Shing, e Kam-Bo Wong. "The Maturation Pathway of Nickel Urease". Inorganics 7, n. 7 (6 luglio 2019): 85. http://dx.doi.org/10.3390/inorganics7070085.

Testo completo

Abstract (sommario):

Maturation of urease involves post-translational insertion of nickel ions to form an active site with a carbamylated lysine ligand and is assisted by urease accessory proteins UreD, UreE, UreF and UreG. Here, we review our current understandings on how these urease accessory proteins facilitate the urease maturation. The urease maturation pathway involves the transfer of Ni2+ from UreE → UreG → UreF/UreD → urease. To avoid the release of the toxic metal to the cytoplasm, Ni2+ is transferred from one urease accessory protein to another through specific protein–protein interactions. One central theme depicts the role of guanosine triphosphate (GTP) binding/hydrolysis in regulating the binding/release of nickel ions and the formation of the protein complexes. The urease and [NiFe]-hydrogenase maturation pathways cross-talk with each other as UreE receives Ni2+ from hydrogenase maturation factor HypA. Finally, the druggability of the urease maturation pathway is reviewed.

Gli stili APA, Harvard, Vancouver, ISO e altri

22

Magerramov, A. M., R. T. Abdinbekova, M. M. Kurbanova, A. V. Zamanova e M. A. Allakhverdiev. "Synthesis of substituted ureas from urea and halohydrins". Russian Journal of Applied Chemistry 77, n. 10 (ottobre 2004): 1667–69. http://dx.doi.org/10.1007/s11167-005-0093-6.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

23

Gruninger, Stephen E., e Manuel Goldman. "Evidence for urea cycle activity in Sporosarcina ureae". Archives of Microbiology 150, n. 4 (agosto 1988): 394–99. http://dx.doi.org/10.1007/bf00408313.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

24

Akgun, Ugur. "Mechanism of Urea Conduction through H. Pylori UreI". Biophysical Journal 110, n. 3 (febbraio 2016): 545a. http://dx.doi.org/10.1016/j.bpj.2015.11.2917.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

25

Hong, Wu, Kouichi Sano, Shinichi Morimatsu, David R. Scott, David L. Weeks, George Sachs, Toshiyuki Goto et al. "Medium pH-dependent redistribution of the urease of Helicobacter pylori". Journal of Medical Microbiology 52, n. 3 (1 marzo 2003): 211–16. http://dx.doi.org/10.1099/jmm.0.05072-0.

Testo completo

Abstract (sommario):

Helicobacter pylori is an aetiological agent of gastric disease. Although the role of urease in gastric colonization of H. pylori has been shown, it remains unclear as to where urease is located in this bacterial cell. The purpose of this study was to define the urease-associated apparatus in the H. pylori cytoplasm. H. pylori was incubated at both a neutral and an acidic pH in the presence or absence of urea and examined by double indirect immunoelectron microscopy. The density of gold particles for UreA was greatest in the inner portion of the wild-type H. pylori cytoplasm at neutral pH but was greatest in the outer portion at acidic pH. This difference was independent of the presence of urea and was not observed in the ureI-deletion mutant. Also, the eccentric shift of urease in acidic pH was not observed in UreI. After a 2 day incubation period at acidic pH, it was observed that the urease gold particles in H. pylori assembled and were associated with UreI gold particles. Urease immunoreactivity shifted from the inner to the outer portion of H. pylori as a result of an extracellular decrease in pH. This shift was urea-independent and UreI-dependent, suggesting an additional role of UreI in urease-dependent acid resistance. This is the first report of the intracellular transport of molecules in bacteria in response to changes in the extracellular environment.

Gli stili APA, Harvard, Vancouver, ISO e altri

26

Bussink, D. W., e O. Oenema. "Differences in rainfall and temperature define the use of different types of nitrogen fertilizer on managed grassland in UK, NL [Netherlands] and Eire". Netherlands Journal of Agricultural Science 44, n. 4 (1 dicembre 1996): 317–38. http://dx.doi.org/10.18174/njas.v44i4.540.

Testo completo

Abstract (sommario):

There are distinct differences between the Netherlands (NL) and the United Kingdom (UK) in the use of urea and calcium ammonium nitrate (Ca-AmmN) fertilizers on grassland. It has been known for some time that rainfall and temperature affect NH3 volatilization from urea and its agronomic efficiency. This study aimed (i) to examine rainfall and temperature pattern in NL and UK in relation to the observed urea efficiency, and (ii) to provide a simple decision support model for farmers to enable them to choose the most appropriate N fertilizer. A statistical analysis (residual maximum likelihood) of existing data from numerous field trials was undertaken. The agronomic efficiency of urea compared to Ca-AmmN in field trials was expressed as (i) urea relative N yield (Urel-N-y), and (ii) apparent-urea relative (N) yield (Uarel-(N)-y). In NL, (Urel-N-y) did not significantly differ from 100% on peat grassland. Mean (Urel-N-y) on sand and clay was 95%, in both cases. Mean seasonal Uarel-y and Uarel-N-y for the summed data of sand and clay soils was 92.3 and 86.4%, respectively, without significant differences between first and later cuts. There was no significant improvement of UNapp-relY in the last decades. In the first cut, mean Uarel-y was lower than in UK (100.9%) and Eire (100.2%). Differences in efficiency between countries could be described by short-term rainfall and temperature. By aggregating NL, UK and Eire data a simple regression equation was derived: Uarel-y= 89.48(+or-0.78) +[2.188(+or-0.15)xR3] -[1.091(+or-0.07)xT3], where R3 and T3 are rainfall amount and average temperature within three days after fertilizer application, respectively. The decision support model based on this equation showed that under prevailing NL weather conditions it will be profitable for the farmer to apply urea instead of calcium ammonium nitrate, for the first and second cut, only once every 5 and 7 years, respectively, because R3's exceeding 6 and 9.5 mm are required.

Gli stili APA, Harvard, Vancouver, ISO e altri

27

Zhao, Hui, Richard B. Thompson, Virginia Lockatell, David E. Johnson e Harry L. T. Mobley. "Use of Green Fluorescent Protein To Assess Urease Gene Expression by Uropathogenic Proteus mirabilis during Experimental Ascending Urinary Tract Infection". Infection and Immunity 66, n. 1 (1 gennaio 1998): 330–35. http://dx.doi.org/10.1128/iai.66.1.330-335.1998.

Testo completo

Abstract (sommario):

ABSTRACT Proteus mirabilis, a cause of complicated urinary tract infection, expresses urease when exposed to urea. While it is recognized that the positive transcriptional activator UreR induces gene expression, the levels of expression of the enzyme during experimental infection are not known. To investigate in vivo expression of P. mirabilis urease, the gene encoding green fluorescent protein (GFP) was used to construct reporter fusions. Translational fusions of urease accessory gene ureD, which is preceded by a urea-inducible promoter, were made withgfp (modified to express S65T/V68L/S72A [B. P. Cormack et al. Gene 173:33–38, 1996]). Constructs were confirmed by sequencing of the fusion junctions. UreD-GFP fusion protein was induced by urea in both Escherichia coli DH5α and P. mirabilis HI4320. By using Western blotting with antiserum raised against GFP, expression level was shown to correlate with urea concentration (tested from 0 to 500 mM), with highest induction at 200 to 500 mM urea. Fluorescent E. coli and P. mirabilis bacteria were observed by fluorescence microscopy following urea induction, and the fluorescence intensity of GFP in cell lysates was measured by spectrophotofluorimetry. P. mirabilis HI4320 carrying the UreD-GFP fusion plasmid was transurethrally inoculated into the bladders of CBA mice. One week postchallenge, fluorescent bacteria were detected in thin sections of both bladder and kidney samples; the fluorescence intensity of bacteria in bladder tissue was higher than that in the kidney. Kidneys were primarily infected with single-cell-form fluorescent bacteria, while aggregated bacterial clusters were observed in the bladder. Elongated swarmer cells were only rarely observed. These observations demonstrate that urease is expressed in vivo and that using GFP as a reporter protein is a viable approach to investigate in vivo expression ofP. mirabilis virulence genes in experimental urinary tract infection.

Gli stili APA, Harvard, Vancouver, ISO e altri

28

Yerokun, O. A. "Response of maize to ammonium nitrate, urea and cogranulated urea-urea phosphate". South African Journal of Plant and Soil 14, n. 2 (gennaio 1997): 63–66. http://dx.doi.org/10.1080/02571862.1997.10635083.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

29

Bakibaev, А. А., М. Zh Sadvakassova, V. S. Malkov, R. Sh Еrkasov, A. A. Sorvanov e O. A. Kotelnikov. "Study of the biologically active acyclic ureas by nuclear magnetic resonance". Bulletin of the Karaganda University. "Chemistry" series 100, n. 4 (30 dicembre 2020): 60–74. http://dx.doi.org/10.31489/2020ch4/60-74.

Testo completo

Abstract (sommario):

A wide variety of acyclic ureas comprising alkyl, arylalkyl, acyl, and aryl functional groups are investigated by nuclear magnetic resonance spectroscopy. In general, spectral characteristics of more than 130 substances based on acyclic ureas dissolved in deuterated dimethyl sulfoxide at room temperature are studied. The re-sults obtained based on the studies of 1H and 13C NMR spectra of urea and its N-alkyl-, N-arylalkyl-, N-aryl- and 1,3-diaryl derivatives are presented, and the effect of these functional groups on the chemical shifts in carbonyl and amide moieties in acyclic urea derivatives is discussed. An introduction of any type of substitu-ent (electron-withdrawing or electron-donating) into urea molecule is stated to result in a strong upfield shift in 13C NMR spectra relatively to unsubstituted urea. A strong sensitivity of NH protons to the presence of acyl and aryl groups in nuclear magnetic resonance spectra is pointed out. In some cases, qualitative depend-encies between the chemical shifts in the NMR spectra and the structure of the studied acyclic ureas are re-vealed. A summary of the results on chemical shifts in the NMR spectra of the investigated substances allows determining the ranges of chemical shift variations of the key protons and carbon atoms in acyclic ureas. The literature describing the synthesis procedures are provided. The results obtained significantly expand the methods of reliable identification of biologically active acyclic ureas and their metabolites that makes it promising to use NMR spectroscopy both in biochemistry and in clinical practice.

Gli stili APA, Harvard, Vancouver, ISO e altri

30

Sein, K. T., e G. Arumainayagam. "Correlation between serum urea and salivary urea." Clinical Chemistry 33, n. 12 (1 dicembre 1987): 2303–4. http://dx.doi.org/10.1093/clinchem/33.12.2303.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

31

Kågedal, Bertil. "Why “Urea Nitrogen” When Urea is Measured?" Clinical Chemistry 44, n. 4 (1 aprile 1998): 894–95. http://dx.doi.org/10.1093/clinchem/44.4.894.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

32

RODRIGUES, M., J. PIDLICH, C. MÜLLER e H. SINZINGER. "13C-urea versus 14C-urea breath test". Nuclear Medicine Communications 19, n. 11 (novembre 1998): 1021–22. http://dx.doi.org/10.1097/00006231-199811000-00001.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

33

HART, G. C., e M. P. AVISON. "13C-urea versus 14C-urea breath test". Nuclear Medicine Communications 20, n. 5 (maggio 1999): 495. http://dx.doi.org/10.1097/00006231-199905000-00141.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

34

RODRIGUES, M., J. PIDLICH, C. MULLER e H. SINZINGER. "13C-urea versus 14C-urea breath tests". Nuclear Medicine Communications 20, n. 5 (maggio 1999): 495–96. http://dx.doi.org/10.1097/00006231-199905000-00142.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

35

MILLAR, A. M., e J. HANNAN. "13C-urea versus 14C-urea breath test". Nuclear Medicine Communications 20, n. 7 (luglio 1999): 686. http://dx.doi.org/10.1097/00006231-199907000-00043.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

36

Kaatze, Udo. "Hydration of urea and alkylated urea derivatives". Journal of Chemical Physics 148, n. 1 (7 gennaio 2018): 014504. http://dx.doi.org/10.1063/1.5003569.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

37

Zorc, Branka, Zrinka Rajić e Ivana Perković. "Antiproliferative evaluation of various aminoquinoline derivatives". Acta Pharmaceutica 69, n. 4 (1 dicembre 2019): 661–72. http://dx.doi.org/10.2478/acph-2019-0048.

Testo completo

Abstract (sommario):

Abstract Four classes of aminoquinoline derivatives were prepared: primaquine ureas 1a–f, primaquine bis-ureas 2a–f, chloroquine fumardiamides 3a–f and mefloquine fumardiamides 4a–f. Their antiproliferative activities against breast adeno-carcinoma (MCF-7), lung carcinoma (H460) and colon carcinoma (HCT 116 and SW620) cell lines were evaluated in vitro, using MTT cell proliferation assay. The results revealed a low activity of primaquine urea and bis-urea derivatives and high activity of all fumardiamides, with IC50 values in low micromolar range against all tested cancer cell lines.

Gli stili APA, Harvard, Vancouver, ISO e altri

38

Chakraborty, Ranabir, T. J. Purakayastha, B. Ramakrishnan, Babanpreet Kour, Arpan Bhowmik e Abinash Das. "Long Term Effect of Residue Management, Nitrification and Urease Inhibitor on Non-target Soil Bacterial Community in Rice–Wheat and Maize–Wheat Cropping Systems". International Journal of Bio-resource and Stress Management 15, July, 7 (21 luglio 2024): 01–13. http://dx.doi.org/10.23910/1.2024.5393.

Testo completo

Abstract (sommario):

An investigation was carried out from November, 2020 to April, 2021 at the Indian Agricultural Research Institute, New Delhi, employing a split-split plot layout with two cropping systems (rice-wheat and maize-wheat), four long-term crop residue management strategies including burning (CRB), removal (CRR), incorporation (CRI), and biochar (BC), and two nitrogen management: neem-coated urea (NCU) and Urea+dual (urease+nitrification) inhibitor (UUINI). Soil DNA was extracted and quantified for 16S bacteria, 16S archaea, nifH, ureC and anammox abundances using quantitative PCR. Additionally, Soil samples were analysed for available nitrogen (urea, NH4+, NO3-) and water-soluble carbon. Rice-wheat rotations favoured higher 16S bacterial abundance while maize-wheat elevated 16S archaea. Notably, CRI and BC exhibited higher bacterial abundance compared to CRR and CRB, while minimal impact was noticed for archaea. The nifH gene abundance was influenced by all treatments along with their interactions. UreC gene copies exhibited a direct relationship with 16S archaea and an inverse relationship with 16S bacteria; UUINI showed a higher abundance of ureC under CRI and BC in both cropping systems. Moreover, anammox abundance correlated positively with NH4+ and NO3- but negatively with unhydrolyzed urea, indicating the inhibitory effect of UUINI. These findings underscore the complex relationships among inhibitors, residue management, cropping systems and soil microbial communities, emphasizing the need for tailored approaches to optimise nutrient cycling and soil health in agricultural systems.

Gli stili APA, Harvard, Vancouver, ISO e altri

39

Carter, Eric L., e Robert P. Hausinger. "Characterization of the Klebsiella aerogenes Urease Accessory Protein UreD in Fusion with the Maltose Binding Protein". Journal of Bacteriology 192, n. 9 (5 marzo 2010): 2294–304. http://dx.doi.org/10.1128/jb.01426-09.

Testo completo

Abstract (sommario):

ABSTRACT Assembly of the Klebsiella aerogenes urease metallocenter requires four accessory proteins, UreD, UreE, UreF, and UreG, to effectively deliver and incorporate two Ni2+ ions into the nascent active site of the urease apoprotein (UreABC). Each accessory protein has been purified and characterized with the exception of UreD due to its insolubility when it is overproduced in recombinant cells. In this study, a translational fusion was made between the maltose binding protein (MBP) and UreD, with the resulting MBP-UreD found to be soluble in Escherichia coli cell extracts and able to complement a ΔureD-urease cluster in this host microorganism. MBP-UreD was purified as a large multimer (>670 kDa) that bound approximately 2.5 Ni2+ ions (Kd of ∼50 μM, where Kd is the dissociation constant) per UreD protomer according to equilibrium dialysis measurements. Zn2+ directly competes with 10-fold higher affinity (∼4 Zn2+ ions per protomer; Kd of 5 μM) for the Ni2+ binding sites. MBP pulldown experiments demonstrated that the UreD domain of MBP-UreD formed in vivo complexes with UreF, UreG, UreF plus UreG, or UreABC when these proteins were overproduced in the same E. coli cells. In addition, a UreABC-(MBP-UreD)-UreFG complex was observed in cells producing all urease components. Comparative in vitro binding experiments with purified proteins demonstrated an approximate 1:1 binding ratio between the UreD domain of MBP-UreD and the UreF domain of the UreEF fusion, only weak or transient interaction between MBP-UreD and UreG, and no binding with UreABC. These studies are the first to describe the properties of purified UreD, and they extend our understanding of its binding partners both in vitro and in the cell.

Gli stili APA, Harvard, Vancouver, ISO e altri

40

Masaaki Minami, Shin-nosuke Hashikawa, Takafumi Ando, Hiroshi Kobayashi, Hidemi Goto e Michio Ohta. "Involvement of CO2 generated by urease in multiplication of Helicobacter pylori". GSC Advanced Research and Reviews 7, n. 3 (30 giugno 2021): 045–53. http://dx.doi.org/10.30574/gscarr.2021.7.3.0123.

Testo completo

Abstract (sommario):

Helicobacter pylori (H. pylori) urease generates both ammonia (NH3) and carbon dioxide (CO2) from urea. NH3 helps H. pylori to survive in the stomach in part by neutralizing gastric acid. However, the relationship between CO2 and H. pylori is not completed cleared. We examined the effect of CO2 generated by urease on multiplication of H. pylori by using isogenic ureB mutant and ureB complemented strain from H. pylori strain JP26. Wild-type strain survived in the medium supplement with 1mM urea in room air, however, the urease negative strain did not. To discern whether CO2 was incorporated into H. pylori, 14C in bacillus was counted after 6 hours incubation with 14C urea in both acidic and neutral medium. Significant more 14C uptake was detected in wild-type strain compared to ureB mutant strain and this uptake in the wild-type strain was more under acidic condition compared to under neutral condition, but no difference was identified in the mutant strain. These results suggest that CO2 generated by urease plays a role in multiplication of H. pylori.

Gli stili APA, Harvard, Vancouver, ISO e altri

41

Simioni, F., e M. Modesti. "Glycolysis of Flexible Polyurethane Foams". Cellular Polymers 12, n. 5 (settembre 1993): 337–48. http://dx.doi.org/10.1177/026248939301200501.

Testo completo

Abstract (sommario):

Flexible water blown polyurethanes are polymers with repeating urethane and urea groups. When they undergo heating in the presence of glycols the reaction of these groups leads to soluble products. The transesterification reaction of the urethane groups, that leads to the formation of new carbamate is faster than that of the urea groups. Carbamates in turn undergo aminolysis due to the amines formed in the glycolysis of the urea groups. The use of ethylene glycol (EG) allows the process to be carried out with high polymer/glycol ratio (up to 4:1). A polyphase product is obtained with a top liquid phase mainly formed by the polyether polyol from the polymer, an intermediate liquid phase formed by the solution of carbamates, ureas and amines in EG and a bottom solid phase with compounds with prevalent urea bonds.

Gli stili APA, Harvard, Vancouver, ISO e altri

42

Kraus, George A., Dan Bougie, Robert A. Jacobson e Yingzhong Su. "The urea connection. Intramolecular Diels-Alder reactions of ureas". Journal of Organic Chemistry 54, n. 10 (maggio 1989): 2425–28. http://dx.doi.org/10.1021/jo00271a035.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

43

Shevchuk, A. V., V. F. Matyushov, Yu V. Maslak e V. F. Rosovitskii. "Segmented polyurethane-ureas with N-cyanoethyl-substituted urea groups". Polymer Science U.S.S.R. 30, n. 2 (gennaio 1988): 277–81. http://dx.doi.org/10.1016/0032-3950(88)90119-0.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

44

WOOD, CHRIS M., R. S. MUNGER e D. P. TOEWS. "Ammonia, Urea and H+ Distribution and the Evolution of Ureotelism in Amphibians". Journal of Experimental Biology 144, n. 1 (1 luglio 1989): 215–33. http://dx.doi.org/10.1242/jeb.144.1.215.

Testo completo

Abstract (sommario):

In theory, the distribution of ammonia across cell membranes (Tammi/Tamme) between intracellular and extracellular fluids (ICF and ECF) may be determined by the transmembrane pH gradient (as in mammals), the transmembrane potential (as in teleost fish), or both, depending on the relative permeability of the membranes to NH3 and NH4+ (pNH3/pNH4+). The resting distributions of H+ (via [14C]DMO), ammonia and urea between plasma and skeletal muscle, and the relative excretion rates of ammonia-N and urea-N, were measured in five amphibian species (Bufo marinus, Ambystoma tigrinum, Rana catesbeiana, Necturus maculosus and Xenopus laevis). Although ureai/ureae ratios were uniformly close to 1.0, Tammi/Tamme. ratios correlated directly with the degree of ammoniotelism in each species, ranging from 9.1 (Bufo, 10% ammoniotelic) to 16.7 (Xenopus, 79% ammoniotelic). These values are intermediate between ratios of about 30 (low pNH3/pNH4+) in ammoniotelic teleost fish and about 3 (high pNH3/pNH4+) in ureotelic mammals. The results indicate that amphibians represent a transitional stage in which ammonia distribution is influenced by both the pHi-pHe gradient and the membrane potential, and that a reduction in cell membrane permeability to NH4+ (i.e. increased pNH3/pNH4+) was associated with the evolution of ureotelism. Hyperosmotic saline exposure increased urea excretion 10-fold in Xenopus, while ammonia excretion remained unchanged. Tammi/Tamme fell, but this response was attributable to an abolition of the pHi-pHe gradient, rather than a physiological change in the cell membrane pNH3/pNH4+.

Gli stili APA, Harvard, Vancouver, ISO e altri

45

Sachs, George, David L. Weeks, Yi Wen, Elizabeth A. Marcus, David R. Scott e Klaus Melchers. "Acid Acclimation byHelicobacter pylori". Physiology 20, n. 6 (dicembre 2005): 429–38. http://dx.doi.org/10.1152/physiol.00032.2005.

Testo completo

Abstract (sommario):

Helicobacter pylori is a Gram-negative neutralophile associated with peptic ulcers and gastric cancer. It has a unique ability to colonize the human stomach by acid acclimation. It uses the pH-gated urea channel, UreI, to enhance urea access to intrabacterial urease and a membrane-anchored periplasmic carbonic anhydrase to regulate periplasmic pH to ~6.1 in acidic media, whereas other neutralophiles cannot regulate periplasmic pH and thus only transit the stomach.

Gli stili APA, Harvard, Vancouver, ISO e altri

46

&NA;. "Acetylcysteine/urea". Reactions Weekly &NA;, n. 1391 (marzo 2012): 5. http://dx.doi.org/10.2165/00128415-201213910-00014.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

47

SINGH, M., N. VERMA, A. GARG e N. REDHU. "Urea biosensors". Sensors and Actuators B: Chemical 134, n. 1 (28 agosto 2008): 345–51. http://dx.doi.org/10.1016/j.snb.2008.04.025.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

48

Fröhlich, Otto. "Urea Transport". Journal of Membrane Biology 212, n. 2 (settembre 2006): 69–70. http://dx.doi.org/10.1007/s00232-006-0866-8.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

49

Meessen, Jozef. "Urea synthesis". Chemie Ingenieur Technik 86, n. 12 (10 novembre 2014): 2180–89. http://dx.doi.org/10.1002/cite.201400064.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

50

Sanchary, Ishrat Jahan, e Shah Muhammad Imamul Huq. "Efficiency of Black Urea Fertilizer over White Urea". Journal of Agricultural Studies 6, n. 1 (27 dicembre 2017): 45. http://dx.doi.org/10.5296/jas.v6i1.12372.

Testo completo

Abstract (sommario):

To reduce the loss of nitrogen and to improve cost effectiveness as well as plant nitrogen content, a humic acid coated urea fertilizer, called Black Urea is used in the present experiment. Four sets of pot experiment was conducted here to compare the efficiency of black urea fertilizer over conventional white urea. Kalmi, a fast growing, leafy vegetable, was allowed to grow for 60 days to carry out this experiment. After harvesting, both the root and shoot growth of the plants for all four sets of experiment and the available N and P content was calculated. In addition to that plant protein content was analyzed to draw the conclusion undoubtedly. Black urea was evidenced to posses better efficiency over white urea fertilizer as far as the nutritional quality and cost of the experiment was concerned.

Gli stili APA, Harvard, Vancouver, ISO e altri

Offriamo sconti su tutti i piani premium per gli autori le cui opere sono incluse in raccolte letterarie tematiche. Contattaci per ottenere un codice promozionale unico!