Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:6.3.4.6 (urease)
7,490 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Urease was purified 24-fold from extracts of Klebsiella aerogenes. The enzyme has a molecular weight of 230,000 as determined by gel filtration, is highly substrate specific, and has a Km for urea of 0.7 mM. A mutant strain lacking urease was isolated; it failed to grow with urea as the sole source of nitrogen but did grow on media containing other nitrogen sources such as ammonia, histidine, or arginine. Urease was present at a high level when the cells were starved for nitrogen; its synthesis was repressed when the external ammonia concentration was high. Formation of urease did not require induction by urea and was not subject to catabolite repression. Its synthesis was controlled by glutamine synthetase. Mutants lacking glutamine synthetase failed to produce urease, and mutants forming glutamine synthetase at a high constitutive level also formed urease constitutively. Thus, the formation of urease is regulated like that of other enzymes of K. aerogenes capable of supplying the cell with ammonia or glutamate.
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PMID:Urease of Klebsiella aerogenes: control of its synthesis by glutamine synthetase. 1 38

We have partially characterized the biochemical parameters of glutamine synthetase from Klebsiella pneumoniae and have shown that the differential affinity of adenylylated and unadenylylated glutamine synthetase for adenosine diphosphate provides a convenient means of determining the adenylylation state. Using this assay procedure, we examined the relationship between the adenylylation state and the expression of other genes involved in nitrogen assimilation. We observed no correlation between the adenylylation state and the expression of histidase, glutamine synthetase, glutamate synthase, glutamate dehydrogenase, and urease in aerobic cultures.
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PMID:Relation between the adenylylation state of glutamine synthetase and the expression of other genes involved in nitrogen metabolism. 3 15

The energy-dependent urea permease was studied in two strains of Pseudomonas aeruginosa, measuring the uptake (transport and metabolism) of 14C-urea. In both strains urea uptake in vivo and urease activity in vitro differed significantly with respect to kinetic parameters, temperature and pH dependence and response to metabolic inhibitors. Ammonium strongly interfered both with the expression of the urea uptake system and its activity. The inhibition of the uptake activity by ammonium was partially relieved by hydraziniumsulfate, which prevented the translocation of ammonium into the cell, and in a methylammonium/ammonium transport-defective mutant of strain DSM 50071. Furthermore, methionine-sulfoximine, which prevented the intracellular glutamine formation from ammonium via inhibition of glutamine synthetase, relieved the inhibition of urea uptake by ammonium. These findings suggested that urea uptake activity in P. aeruginosa is regulated by intracellular glutamine.
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PMID:Regulation of urea uptake in Pseudomonas aeruginosa. 135 27

The levels of urease and asparaginase were elevated 25- and 20-fold, respectively, in extracts of Bacillus subtilis cells grown in medium containing nitrogen sources that are poor sources of ammonium (NH4+) compared with the levels seen in extracts of cells grown in medium containing nitrogen sources that are good sources of NH4+. To determine whether a collection of genes whose expression responds to nitrogen availability could be isolated, a library of Tn917-lacZ insertions was screened for nitrogen-regulated beta-galactosidase expression. Two fusion strains were identified. beta-Galactosidase expression was 26- and 4,000-fold higher, respectively, in the nrg-21::Tn917-lacZ and the nrg-29::Tn917-lacZ insertion strains during NH4(+)-restricted growth than during growth on nitrogen sources that are good sources of NH4+. PBS1 transduction analysis showed that the nrg-21::Tn917-lacZ insertion mapped between gutB and purB and that the nrg-29::Tn917-lacZ insertion mapped between degSU and spoIID. The repression of expression of these four gene products during growth on good sources of NH4+ required the wild-type glutamine synthetase protein but not the glutamine synthetase regulatory protein, GlnR.
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PMID:Identification of genes and gene products whose expression is activated during nitrogen-limited growth in Bacillus subtilis. 167 Sep 35

At present in vivo NMR spectroscopic studies of brain glutamate and glutamine concentrations relative to encephalopathy have mainly been performed in hepatic encephalopathy (HE). In vivo proton NMR studies were performed in rats with hyperammonemia and acute HE due to acute liver ischemia as well as in rats with hyperammonemia due to either repeated urease i.p. injection or i.p. administration of methionine sulfoximine, a well known inhibitor of glutamine synthetase. In man, in vivo proton NMR is described in patients with chronic liver disease: cirrhosis of different etiology and associated with different degrees of HE. In the experimental models proton NMR spectroscopy of the cerebral cortex revealed an increase in glutamine concentration, a decrease in glutamate concentration and a decrease in phosphocholine compounds. In humans no clear distinction between cerebral cortex glutamate and glutamine concentration could be made by in vivo 1H NMR spectroscopy. However, the combined glutamate/glutamine peak increased in a way compatible with an increased cerebral cortex glutamine concentration during chronic HE. In the cirrhotic patients too a decrease in cerebral cortex phosphocholine compounds was observed, the explanation of which is unclear. Both the experimental work and the clinical observations support the hypothesis that impairment of the glutamate/glutamine cycle between astrocytes and neurons plays a role in the pathogenesis of hepatic encephalopathy.
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PMID:What the clinician can learn from MR glutamine/glutamate assays. 167 85

A positive, genetic selection against the activity of the nitrogen regulatory (NTR) system was used to isolate insertion mutations affecting nitrogen regulation in Klebsiella aerogenes. Two classes of mutation were obtained: those affecting the NTR system itself and leading to the loss of almost all nitrogen regulation, and those affecting the nac locus and leading to a loss of nitrogen regulation of a family of nitrogen-regulated enzymes. The set of these nac-dependent enzymes included histidase, glutamate dehydrogenase, glutamate synthase, proline oxidase, and urease. The enzymes shown to be nac independent included glutamine synthetase, asparaginase, tryptophan permease, nitrate reductase, the product of the nifLA operon, and perhaps nitrite reductase. The expression of the nac gene was itself highly nitrogen regulated, and this regulation was mediated by the NTR system. The loss of nitrogen regulation was found in each of the four insertion mutants studied, showing that loss of nitrogen regulation resulted from the absence of nac function rather than from an altered form of the nac gene product. Thus we propose two classes of nitrogen-regulated operons: in class I, the NTR system directly activates expression of the operon; in class II, the NTR system activates nac expression and the product(s) of the nac locus activates expression of the operon.
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PMID:Role of the nac gene product in the nitrogen regulation of some NTR-regulated operons of Klebsiella aerogenes. 197 23

The product of the rpoN gene is an alternative sigma factor of RNA polymerase which is required for transcription of a number of genes in members of the family Enterobacteriaceae, including those that specify enzymes of nitrogen assimilation, amino acid uptake, and degradation of a variety of organic molecules. We have previously shown that transcription of the pilin gene of Pseudomonas aeruginosa also requires RpoN (K. S. Ishimoto and S. Lory, Proc. Natl. Acad. Sci. USA 86:1954-1957, 1989) and have undertaken a more extensive survey of genes under RpoN control. Strains of P. aeruginosa that carry an insertionally inactivated rpoN gene were constructed and shown to be nonmotile because of the inability of these mutants to synthesize flagellin. The mutation in rpoN had no effect on expression of extracellular polypeptides, outer membrane proteins, and the alginate capsule. However, the rpoN mutants were glutamine auxotrophs and were defective in glutamine synthetase, indicating defects in nitrogen assimilation. In addition, the P. aeruginosa rpoN mutants were defective in urease activity. These findings indicate that the sigma factor encoded by the rpoN gene is used by P. aeruginosa for transcription of a diverse set of genes that specify biosynthetic enzymes, degradative enzymes, and surface components. These rpoN-controlled genes include pili and flagella which are required for full virulence of the organism.
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PMID:The rpoN gene product of Pseudomonas aeruginosa is required for expression of diverse genes, including the flagellin gene. 215 9

1. The objective of the present experiment was to study the effects of oak (Quercus incana) leaves rich in tannins on various enzyme activities of the bovine rumen. 2. The procedure employed was incubation of tannin-rich, very-low-tannin or virtually tannin-free leaves in nylon-gauze bags in the rumen, and determination of enzyme activities in microbes tightly bound to the solid matrix and in microbes loosely plus tightly attached to the solid matrix. 3. The activities of urease (EC 3.5.1.5), carboxymethylcellulose, glutamate dehydrogenase (EC 1.4.1.2) and alanine aminotransferase (glutamic-pyruvic transaminase) (EC 2.6.1.2) were significantly lower in the tannin-rich group, whereas the activities of glutamate ammonia ligase (glutamine synthetase) (EC 6.3.1.2; both gamma-glutamyltransferase (EC 2.3.2.2) and the forward reaction) were higher in the tannin-rich group. These changes were more marked in micro-organisms tightly bound to the solid matrix than in the more complex microbial compartment. 4. The protein, DNA and RNA contents, and protein: RNA ratio, were significantly lower in the tannin-rich group, whereas no difference was observed for protein: DNA between the groups. 5. Effects of tannin-containing extracts of oak leaves on various rumen enzymes in vitro showed a trend similar to that observed in nylon-gauze bags, suggesting that the changes observed in various compartments were due to the tannins of oak leaves.
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PMID:Effect of tannin-rich leaves of oak (Quercus incana) on various microbial enzyme activities of the bovine rumen. 246 31

We describe a new enzymic colorimetric method in which urea is measured in serum by use of a single reagent mixture. Ammonia produced by urea hydrolysis, catalyzed by urease, reacts with glutamate and ATP in the presence of glutamine synthetase. The ADP so produced is assayed in reactions catalyzed sequentially by pyruvate kinase and pyruvate oxidase in a system that generates hydrogen peroxide. The hydrogen peroxide is measured at 500 or 550 nm in a reaction catalyzed by horseradish peroxidase, with phenol/4-aminophenazone as the chromogen. The reaction is complete in 15 min at 37 degrees C. The standard curve is linear up to a urea concentration of 40 mmol/L. Precision is good; CVs ranged from 2.5% to 3.1%. Results by the present method compared well with those by a candidate Reference Method and are not subject to interferences from commonly used drugs and anticoagulants.
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PMID:Enzymic urea assay: a new colorimetric method based on hydrogen peroxide measurement. 256 17

The levels of several enzymes involved in assimilation of different nitrogen compounds were investigated in Streptomyces clavuligerus in relation to the nitrogen source supplied to the cultures. Threonine dehydratase, serine dehydratase, proline dehydrogenase, histidase and urocanase were not decreased in the presence of ammonium. The latter two enzymes were induced by histidine in the culture medium, while proline dehydrogenase was induced by proline. Glutamine synthetase, urease and ornithine aminotransferase levels were higher with poor nitrogen sources and were repressed by ammonium. Arginase was induced by arginine and repressed by ammonium. Glutamine synthetase was rapidly inactivated upon addition of ammonium to the culture, and could be reactivated in vitro by treatment with snake venom phosphodiesterase, which suggested that adenylylation is involved in the inactivation. Three previously isolated mutants with abnormal glutamine synthetase activities showed pleiotropic effects on urease formation. All these data point to a mechanism controlling preferential utilization of some nitrogen sources in this species.
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PMID:Regulation of nitrogen catabolic enzymes in Streptomyces clavuligerus. 257 37


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