Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.5.1.5 (urease)
 7,257 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Aspergillus nidulans can utilize urea as a sole source of nitrogen but not as a carbon source. Urea is degraded by a urease. Mutation at any one of three genes, ureB, ureC, and ureD, may result in deficient urease activity. The ureB gene is closely linked to ureA, the structural gene for the urea transport protein. The heat lability of ureB- revertant strain, intragenic complementation tests, and the linkage of ureB to ureA suggest that ureB is the urease structural gene. The ureD gene is probably involved in the synthesis or incorporation of a nickel cofactor essential for urease activity. The function of the ureC gene is not known. Urease is not induced but is subject to nitrogen regulation. The urease activities of ammonium-derepressed mutants show that the effector of nitrogen regulation is more likely to be glutamine than ammonium. When glutamine is present in the medium, urease appears to be inactivated by some means which does not involve a newly synthesized protease or a direct interaction between glutamine and urease.
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PMID:The regulation of urease activity in Aspergillus nidulans. 675 31

Hyperammonemia is an important cause of cerebral dysfunction in liver failure. We used two well-established models to induce hyperammonemia in rats, injection of urease and injection of methionine sulfoximine (MSO). Urease gave a 10-fold increase in blood ammonia while MSO, a glutamine synthetase inhibitor, gave a 4-fold increase in blood ammonia with no increase in brain glutamine levels. We observed a 2-fold increase in 5-HT1A receptor (5-HT1A-R) expression ([3H] 8-OH-DPAT binding) in hippocampus, and little change elsewhere, including thalamus in both models, thus eliminating a role for increased glutamine in the receptor induction. In contrast, a 4 to 8-fold increase in 5-HT1A-R mRNA was observed both in hippocampus and thalamus, suggesting some post-transcriptional regulation. In the absence of glutamine, ammonium acetate treatment of a hippocampal cell line which had been engineered to stably express the 5-HT1A-R (HN2-5) gave a 1.5-fold increase in [3H] 8-OH-DPAT binding and a 4-fold increase in the mRNA levels for the 5-HT1A-R. We conclude that the cell line HN2-5 is a good model for studying some of the biochemical sequelae of hyperammonemia and that changes in brain function are not only at the metabolic level, as thought earlier, but can also occur at the transcriptional level.
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PMID:Hyperammonemia increases serotonin 1A receptor expression in both rat hippocampus and a transfected hippocampal cell line, HN2-5. 767 72

Cerebral neurogenic vasodilation is mediated predominantly by nitric oxide (NO). Thus, NO was suggested to be a vasodilator transmitter. In the present study, the possibility that cerebral perivascular nerves can convert citrulline to arginine was examined to ascertain that NO is derived directly from these perivascular nerves. To investigate the uptake of citrulline and its conversion to arginine, both fresh and cold storage-denervated porcine cerebral arteries with or without endothelial cells were incubated at 37 degrees C for 2 hr in Krebs-Ringer bicarbonate buffer containing 0.5 mM purified [14C]ureido-citrulline. The formation of [14C]arginine was measured as 14CO2 by a coupled enzymatic assay involving arginase and urease. The abolishment of nitric oxidergic nerves was verified by NADPH-diaphorase (constitutive NO synthases) histochemical staining method. The results indicated that there was an active conversion of [14C]arginine from [14C]citrulline in nerve-intact arteries denuded of endothelial cells. The conversion was significantly decreased in denervated arteries, accompanied by a significantly reduced citrulline uptake into these denervated arteries. L-Glutamine, but not L-glutamate, gamma-aminobutyric acid, or nitro-L-arginine significantly inhibited the uptake of [14C]citrulline into cerebral perivascular nerves. These data suggest that porcine cerebral vasodilator nerves are nitric oxidergic in nature and citrulline, co-produced with NO by NO synthases from arginine, can be recycled to form arginine in these nerves. The existence of a functional arginine-citrulline cycle may contribute to a constant supply of L-arginine and suggests a neuronal source of NO for inducing cerebral vasodilation.
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PMID:Arginine synthesis from citrulline in perivascular nerves of cerebral artery. 775 95

Urea production by cortical (CCD) and medullary (OMCD) collecting ducts of the rat kidney was measured in vitro by incubating single microdissected pieces of tubule in the presence of L-[guanido-14C]arginine (0.2 mM). The [14C]urea released from the cells was hydrolysed in presence of urease added to the incubation medium and the 14CO2 formed was trapped in KOH and counted. The effect of various amino acids (AA) on urea production was investigated by adding unlabelled AA (either in combination or singly) at concentrations close to those present in blood plasma. A mixture of 17 AA decreased urea production from [14C]arginine by 46% in CCD and by 58% in OMCD. When lysine and proline were omitted from the mixture, the inhibition was less marked (19% in CCD and 43% in OMCD, respectively). When AA were tested singly, lysine induced the larger inhibition (40% in CCD and 45% in OMCD), than ornithine and glutamine (about 15% each, in CCD and OMCD), whereas proline inhibition (7% in CCD, 10% in OMCD) was not statistically significant. Branched-chain amino acids (BCAA) in combination (leucine, isoleucine and valine) also markedly reduced urea production by CCD and OMCD. Their effect was dose dependent. Solubilization of CCD and OMCD cell membranes with Triton X-100 resulted in a twofold increase in urea production by control samples; the relative inhibition (per cent) induced by BCAA was enhanced, whereas that induced by lysine was decreased. The data suggest that, in living tubules, the inhibition obtained with lysine resulted, for a large part, from competition between lysine and arginine for cell uptake via a common membrane carrier, whereas the inhibition induced by BCAA corresponded to an effect on arginase activity itself.
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PMID:Urea production by kidney collecting ducts in vitro: effect of amino acid addition. 805 17

1. The relationship of the decreased caecal urease activity by dietary penicillin to nitrogen utilisation was assessed in chickens fed a low protein diet plus urea. 2. Dietary penicillin at 20 and 100 mg/kg decreased anaerobic bacteria counts, urease activity and ammonia concentration in caecal contents (P < 0.05, except for ammonia in the case of the 100 mg/kg penicillin diet). 3. The 20 mg/kg penicillin diets significantly increased the excretion of urea and total nitrogen (P < 0.05) and decreased ammonia excretion, and significantly reduced nitrogen retention (P < 0.05). The 100 mg/kg penicillin diet also resulted in similar but not significant changes, which tended to be less than those by the 20 mg/kg penicillin diet. 4. Ammonia, urea, glutamine and uric acid concentrations in blood, liver and kidney were unchanged by dietary penicillin. 5. It is concluded that caecal ammonia production from urea was closely correlated with nitrogen utilisation in chickens fed a low protein diet plus urea.
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PMID:Relationship of decreased caecal urease activity by dietary penicillin to nitrogen utilisation in chickens fed on a low protein diet plus urea. 819 93

Helicobacter pylori has one of the highest urease activities of all known bacteria. Its enzymatic production of ammonia protects the organism from acid damage by gastric juice. The possibility that the urease activity allows the bacterium to utilise urea as a nitrogen source for the synthesis of amino acids was investigated. H. pylori (NCTC 11638) was incubated with 50 mM urea, enriched to 5 atom% excess 15N, that is the excess enrichment of 15N above the normal background, in the presence of either NaCl pH 6.0, or 0.2M citrate pH 6.0. E. coli (NCTC 9001) was used as a urease-negative control. 15N enrichment was detected by isotope ratio mass spectrometry. H. pylori showed intracellular incorporation of 15N in the presence of citrate buffer pH 6.0 but there was no significant incorporation of 15N in unbuffered saline or by E. coli in either pH 6.0 citrate buffer or unbuffered saline. The intracellular fate of the urea-nitrogen was determined by means of gas chromatography/mass spectrometry following incubation with 15N enriched 5 mM urea in the presence of either 0.2 M citrate buffer pH 6.0 or 0.2 M acetate buffer pH 6.0. After 5 min incubation in either buffer the 15N label appeared in glutamate, glutamine, phenylalanine, aspartate and alanine. It appears, therefore, that at pH and urea concentrations typical of the gastric mucosal surface, H. pylori utilises exogenous urea as a nitrogen source for amino acid synthesis. The ammonia produced by H. pylori urease activity thus facilitates the organism's nitrogen metabolism at neutral pH as well as protecting it from acid damage at low pH.
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PMID:Helicobacter pylori utilises urea for amino acid synthesis. 882 3

Helicobacter pylori urease, produced in abundance, is indispensable for the survival of H. pylori in animal hosts. Urea is hydrolyzed by the enzyme, resulting in the liberation of excess ammonia, some of which neutralizes gastric acid. The remaining ammonia is assimilated into protein by glutamine synthetase (EC 6.3.1.2), which catalyzes the reaction: NH3 + glutamate + ATP-->glutamine + ADP + Pi. We hypothesized that glutamine synthetase plays an unusually critical role in nitrogen assimilation by H. pylori. We developed a phenotypic screen to isolate genes that contribute to the synthesis of a catalytically active urease. Escherichia coli SE5000 transformed with plasmid pHP808 containing the entire H. pylori urease gene cluster was cotransformed with a pBluescript plasmid library of the H. pylori ATCC 43504 genome. A weakly urease-positive 9.4-kb clone, pUEF728, was subjected to nucleotide sequencing. Among other genes, the gene for glutamine synthetase was identified. The complete 1,443-bp glnA gene predicts a polypeptide of 481 amino acid residues with a molecular weight of 54,317; this was supported by maxicell analysis of cloned glnA expressed in E. coli. The top 10 homologs were all bacterial glutamine synthetases, including Salmonella typhimurium glnA. The ATP-binding motif GDNGSG (residues 272 to 277) of H. pylori GlnA exactly matched and aligned with the sequence in 8 of the 10 homologs. The adenylation site found in the top 10 homologs (consensus sequence, NLYDLP) is replaced in H. pylori by NLFKLT (residues 405 to 410). Since the Tyr (Y) residue is the target of adenylation and since the H. pylori glutamine synthetase lacks that residue in four strains examined, we conclude that no adenylation occurs within this motif. Cloned H. pylori glnA complemented a glnA mutation in E. coli, and GlnA enzyme activity could be measured spectrophotometrically. In an attempt to produce a GlnA-deficient mutant of H. pylori, a kanamycin resistance cassette was cloned into the Tth111I site of H. pylori glnA. By using the standard technique of allelic exchange mutagenesis, no verifiable glutamine synthetase double-crossover mutant of strain UMAB41 could be isolated, suggesting that the mutation is lethal. We conclude that glutamine synthetase is critical for nitrogen assimilation in H. pylori and is active under all physiologic conditions.
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PMID:Helicobacter pylori glutamine synthetase lacks features associated with transcriptional and posttranslational regulation. 957 59

Axenic mycelia of the ectomycorrhizal basidiomycete, Suillus bovinus, were grown in liquid media under continuous aeration with compressed air at 25 degrees C in darkness. Provided with glucose as the only carbohydrate source, they produced similar amounts of dry weight with ammonia, with nitrate or with alanine, 60-80% more with glutamate or glutamine, but about 35% less with urea as the respectively only exogenous nitrogen source. In crude extracts of cells from NH4(+)-cultures, NADH-dependent glutamate dehydrogenase exhibited high aminating (688 nmol x mg protein(-1) x min(-1)) and low deaminating (21 nmol x mg protein(-1) x min(-1)) activities. Its Km-values for 2-oxoglutarate and for glutamate were 1.43 mM and 23.99 mM, respectively. pH-optimum for amination was about 7.2, that for deamination about 9.3. Glutamine synthetase activity was comparatively low (59 nmol x mg protein(-1) x min(-1)). Its affinity for glutamate was poor (Km = 23.7 mM), while that for the NH4+ replacing NH2OH was high (Km = 0.19 mM). pH-optimum was found at 7.0. Glutamate synthase (= GOGAT) revealed similar low activity (62 nmol x mg protein(-1) x min(-1)), Km-values for glutamine and for 2-oxoglutarate of 2.82 mM and 0.28 mM, respectively, and pH-optimum around 8.0. Aspartate transaminase (= GOT) exhibited similar affinities for aspartate (Km = 2.55 mM) and for glutamate (Km = 3.13 mM), but clearly different Km-values for 2-oxoglutarate (1.46 mM) and for oxaloacetate (0.13 mM). Activity at optimum pH of about 8.0 was 506 nmol x mg protein(-1) x min(-1) for aspartate conversion, but only 39 nmol x mg protein(-1) x min(-1) at optimum pH of about 7.0 for glutamate conversion. Activity (599 nmol x mg protein(-1) x min(-1)), substrate affinities (Km for alanine = 6.30 mM, for 2-oxoglutarate = 0.45 mM) and pH-optimum (6.5-7.5) proved alanine transaminase (= GPT) also important in distribution of intracellular nitrogen. There was comparatively low activity of the obviously constitutive enzyme, urease, (42 nmol x mg protein(-1) x min(-1)) whose substrate affinity was rather high (Km = 0.56 mM). Nitrate reductase proved substrate induced; activity could only be measured after exposure of the mycelia to exogenous nitrate. Routes of entry of exogenous nitrogen and tentative significance of the various enzymes in cell metabolism are discussed.
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PMID:Investigations into enzymes of nitrogen metabolism of the ectomycorrhizal basidiomycete, Suillus bovinus. 1081 9

Nitrogen sources commonly used by cyanobacteria include ammonium, nitrate, nitrite, urea and atmospheric N(2), and some cyanobacteria can also assimilate arginine or glutamine. ABC (ATP-binding cassette)-type permeases are involved in the uptake of nitrate/nitrite, urea and most amino acids, whereas secondary transporters take up ammonium and, in some strains, nitrate/nitrite. In cyanobacteria, nitrate and nitrite reductases are ferredoxin-dependent enzymes, arginine is catabolized by a combination of the urea cycle and arginase pathway, and urea is degraded by a Ni(2+)-dependent urease. These pathways provide ammonium that is incorporated into carbon skeletons through the glutamine synthetase-glutamate synthase cycle, in which 2-oxoglutarate is the final nitrogen acceptor. The expression of many nitrogen assimilation genes is subjected to regulation being activated by the nitrogen-control transcription factor NtcA, which is autoregulatory and whose activity appears to be influenced by 2-oxoglutarate and the signal transduction protein P(II). In some filamentous cyanobacteria, N(2) fixation takes place in specialized cells called heterocysts that differentiate from vegetative cells in a process strictly controlled by NtcA.
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PMID:Nitrogen assimilation and nitrogen control in cyanobacteria. 1566 95

Growth of a glutamine synthetase-deficient mutant of Streptococcus thermophilus was compared to that of the parent strain in milk that was not supplemented or was supplemented with ammonium chloride, glutamine, or the urease inhibitor flurofamide. It was concluded that one of the functions of urease is to supply ammonia for the synthesis of glutamine.
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PMID:Glutamine synthesis is essential for growth of Streptococcus thermophilus in milk and is linked to urea catabolism. 1593 46


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