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)

The existence of Helicobacter pylori in the biliary tract was investigated. Seven bile samples were included in this study. Among them, six bile samples were collected by percutaneous transhepatic cholangiodrainage and the other by needle aspiration during cholecystectomy. Using nested PCR with two sets of primers homologous to the urease A gene, Helicobacter pylori DNA was detected. Three samples, one from a patient with advanced gastric cancer involving the pancreatic head and two from patients with pancreatic head tumor, were found to be positive for Helicobacter pylori DNA. On the other hand, three samples from patients with cholangiocarcinoma and one from a patient with chronic cholecystitis were all negative. To further verify the specificity of our PCR analysis, partial sequences of the PCR products from the three positive samples were analyzed by direct sequencing. Several silent mutations and a missense mutation (AAA to AGA; Lys-164 to Arg-164) were identified in the urease A gene. We conclude that Helicobacter pylori DNA can be easily detected in the bile samples. The possibility of asymptomatic cholangitis caused by this organism requires further investigation.
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PMID:Detection and partial sequence analysis of Helicobacter pylori DNA in the bile samples. 758 92

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

In Arabidopsis thaliana, urease transcript levels increased sharply between 2 and 4 d after germination (DAG) and were maintained at maximal levels until at least 8 DAG. Seed urease specific activity declined upon germination but began to increase in seedlings 2 DAG, reaching approximately 75% of seed activity by 8 DAG. Urea levels showed a small transient increase 1 DAG and then approximately paralleled urease activity, reaching maximal levels at approximately 9 DAG. Urease inhibition with phenylphosphorodiamidate resulted in a 2- to 4-fold increase in urea levels throughout seedling development. Arginine pools (0-8 DAG) changed approximately in parallel with the urea pool. Consistent with arginine being a major source of urea, arginase activity increased 10-fold in the interval 0 to 6 DAG. Allopurinol, a xanthine dehydrogenase inhibitor, had no effect on urea levels up to 3 DAG but reduced the urea pool by 30 to 40% during the interval 5 to 8 DAG, suggesting that purine degradation contributed to the urea pool well after germination, if at all. in aged Arabidopsis seeds, there was correlation between phenylphosphorodiamidate inactivation of urease and germination inhibition, the latter overcome by NH4NO3 or amino acids. Since urease activity, urea precursor, and urea increase in young seedlings, and since urease inactivation results in a nitrogen-reversible inhibition of germination, we propose that urease recycles urea-nitrogen in the seedling.
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PMID:Essential role of urease in germination of nitrogen-limited Arabidopsis thaliana seeds. 777 May 20

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

In the rat kidney, arginine (Arg) synthesis is restricted to the proximal tubule with a decreasing intensity from its convoluted (PCT) to its straight part (PST). The present study was designed to investigate the pattern of Arg synthesis along the nephron in other mammals, the mouse and rabbit. Microdissected representative nephron segments were incubated with 0.1 mM L-[ureido-14C]citrulline in a sealed chamber. Addition of arginase and urease to the incubation medium led to the hydrolysis of Arg into ornithine, NH3, and 14CO2. The latter was trapped in KOH and counted (results are in fmol Arg.min-1.mm tubular length-1). As in the rat, the main site of Arg synthesis in both species was found to be the PCT (mouse, 191; and rabbit, 57). A lower production was observed in rabbit and mouse PST and in rabbit distal segments. Along the PCT (from 1st to 4th mm after the glomerulus), a steep decrease is observed in mouse (595 and 37, respectively) but not in rabbit (57 and 23). The fate of the newly synthesized Arg probably depends on its site of production. Intracellular arginase activity is known to be present in the cortical (C) and medullary (OS) PST, in both mouse and rabbit. In rabbit only, arginase activity is also found in the PCT. We observed that a large part of Arg was further hydrolyzed into urea and ornithine in CPST and OSPST of mouse (66 and 80%, respectively) and rabbit (40 and 70%) but not in rabbit PCT (8%). Thus Arg produced by PCT in both species is probably released in the cortical blood, whereas Arg produced in PST may serve locally to produce urea and ornithine, and the latter could be used for polyamine synthesis.
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PMID:Arginine synthesis in mouse and rabbit nephron: localization and functional significance. 832 90

Arginine metabolism to alkali by the arginine deiminase system in oral bacteria increases their acid tolerance. The potential of urease activity in Streptococcus salivarius to fulfil a similar role was examined. In cell extracts between pH 5.0 and 8.0, urease activity was over 80% the maximal rate. The urease rate was zero at pH 4.3, and at pH 3.6 the enzyme was rapidly inactivated (t 1/2 of 0.6 min). The pH range of intact cells was broader. In Strep. salivarius cells acidified to pH 2.6 for 5 min, urease was completely retained and the ureolytic pH rise was rapid. There was no urease activity after acidification to pH 2. In cells acidified to maintain the pH between 3.3 and 4, viability was maintained for a short period (extrapolation indicated 20 min) and then decreased. This acidification induced alkali generation or acid removal that decreased in parallel to loss of viability. A small fraction (10%) of the urease was rapidly inactivated, after which both the remaining urease and pH response decreased at a similar rate to cell viability (t 1/2 of 15-20 min), but for at least 1 h following acidification, a rapid ureolysis induced rise in pH to above 7. In cells held at pH 3.6 and treated to compromise their membranes by freeze-thawing or transient acidification to pH 2.3, 70-80% of the urease was lost rapidly and the remainder inactivated at a rate similar to that in intact cells. Therefore, although at pH below 4, S. salivarius urease is outside its pH activity range and the free enzyme is rapidly inactivated, intact cells the urease is protected and ureolytic generation of ammonia is capable of substantially raising the pH for at least 1 h while the cell population is being progressively killed by acid.
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PMID:Urease activity in Streptococcus salivarius at low pH. 834 73

We previously reported that guanidino compounds produced by the catabolism of arginine play an important role in the pathophysiology of acute hyperammonemia. In order to understand the metabolism of guanidino compounds during sustained hyperammonemia, we investigated the effect of intraperitoneal urease injection (800 IU/kg) on the levels of guanidino compounds in blood, liver, kidney, and brain of rats. Control rats received an equal volume of saline. Eight hours following injection, rats were sacrificed and blood and tissues were removed. Ammonia and urea were determined by enzymatic and colorimetric assays, respectively. Guanidino compounds were analyzed by high-performance liquid chromatography. Blood and tissue ammonia were significantly increased and urea decreased in urease-treated animals. Blood and kidney arginine levels were significantly decreased although hepatic arginine was increased following urease injection. Elevated hepatic arginine may be due to the rapid conversion of urea to ammonia by urease and the development of a futile urea cycle. Catabolites produced by the transamidination of arginine were significantly decreased in the blood, liver, kidney, and brain of urease-treated rats, whereas acetylation of hepatic arginine to alpha-N-acetylarginine was increased. Blood and tissue guanidinosuccinic acid levels were not elevated during urease induced hyperammonemia, supporting the hypothesis that urea is a precursor for the synthesis of guanidinosuccinic acid.
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PMID:Effect of urease-induced hyperammonemia on metabolism of guanidino compounds. 843 50

The urease from the ascomycetous fission yeast Schizosaccharomyces pombe was purified about 4000-fold (34% yield) to homogeneity by acetone precipitation, ammonium sulfate precipitation, DEAE-Sepharose ion-exchange column chromatography, and if required, Mono-Q ion-exchange fast protein liquid chromatography. The enzyme was intracellular and only one species of urease was detected by nondenaturing polyacrylamide gel electrophoresis (PAGE). The native enzyme had a M(r) of 212 kDa (Sepharose CL6B-200 gel filtration) and a single subunit was detected with a M(r) of 102 kDa (PAGE with sodium dodecyl sulfate). The subunit stoichiometry was not specifically determined, but the molecular mass estimations indicate that the undissociated enzyme may be a dimer of identical subunits. The specific activity was 700-800 micromols urea.min-1.mg protein-1, the optimum pH for activity was 8.0, and the Km for urea was 1.03 mM. The sequence of the amino terminus was Met-Gln-Pro-Arg-Glu-Leu-His-Lys-Leu-Thr-Leu-His-Gln-Leu-Gly-Ser-Leu-Ala and the sequence of two tryptic peptides of the enzyme were Phe-Ile-Glu-Thr-Asn-Glu-Lys and Leu-Tyr-Ala-Pro-Glu-Asn-Ser-Pro-Gly-Phe-Val-Glu-Val-Leu-Glu-Gly-Glu-Ile- Glu- Leu-Leu-Pro-Asn-Leu-Pro. The N-terminal sequence and physical and kinetic properties indicated that S. pombe urease was more like the plant enzymes than the bacterial ureases.
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PMID:Purification and characterization of urease from schizosaccharomyces pombe. 874 56

Urease and ammonia (NH4OH) have been proposed to be play a major role in the pathogenesis of the the Helicobacter pylori (Hp)-associated gastric damage but the mechanism of this damage has not been fully explained. This study was designed the determine whether topical application with NH4OH at low concentration or the generation of the NH4OH in gastric lumen by the hydrolysis of urea in the presence of urease can induce adaptive cytoprotection. Single insult of NH4OH alone in various concentrations (15-500 mM) caused the mucosal damage starting at 30 mM and reaching at 250 mM the value similar to that obtained with 100% ethanol and being accompanied by the fall in gastric blood flow to about 30% of the normal value. When the mucosa was first exposed to the low concentration (15 mM) of NH4OH, causing by itself only small microscopic damage of surface epithelium, but then insulted by a high concentration (250 mM) of NH4OH, the extent of mucosal damage was greatly attenuated as compared to that caused by NH4OH alone. This "adaptive" cytoprotection, accompanied by the rise in the GBF, was reversed in part, after the pretreatment with indomethacin to inhibit PG-cyclooxygenase, with L-NAME to suppress NO-synthase or with capsaicin to induce deactivation of sensory nerves. The combined topical pretreatment with urea (2%) and urease (100 U) to generate NH4OH in the stomach, also significantly reduced the severity of gastric lesions induced by 100% ethanol and this was also accompanied by a significant rise in the gastric blood flow. The protective and hyperemic effects of urea and urease were significantly attenuated by the pretreatment with indomethacin or suppression of NO-synthase by L-NAME. The functional ablation of sensory nerves by the pretreatment with capsaicin also reversed, in part, the protective effect of the combination of urea plus urease and abolished completely the mucosal hyperemia accompanying this protection. We conclude that 1) NH4OH alone at higher concentrations damages the gastric mucosa but when applied at lower concentration corresponding to that in the stomach of Hp-infected patients, or generated by the urea in the presence of urease, NH4OH acts like "mild irritant" to induce adaptive cytoprotection, 2) this adaptive cytoprotection is mediated, in part, by endogenous PG, sensory nerves and arginine-NO-dependent pathway.
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PMID:Adaptive cytoprotection by ammonia and urea-urease system in the rat gastric mucosa. 877 Jul 91

Ammonia (NH4OH) generated by urease from urea in the Helicobacter pylori (Hp)-infected stomach is considered as a one of the major pathogenic factors in the Hp-associated gastritis but the mechanism of the deleterious action of NH4OH on gastric mucosa has not been fully explained. In this study, the gastric mucosa was exposed to topical NH4OH in various concentrations (15-250 mM) (series A) and to NH4OH in a small concentration followed by a high concentration (250 mM) of NH4OH (series B) or to the combination of urea and urease to generate NH4OH (series C) followed by 250 mM NH4OH in order to determine the "mild irritant" and protective properties of this substance on the mucosa. Administration of NH4OH alone resulted in a concentration-dependent mucosal damage starting at 30 mM and reaching at 250 mM the degree similar to that obtained with 100% ethanol. The acute mucosal damage by NH4OH was accompanied by the fall in gastric blood flow reaching nadir at 250 mM NH4OH of about 30% of the normal value. When the mucosa was first exposed to low concentration of NH4OH (15 mM) and then insulted with its larger concentration (250 mM), the lesion area was markedly reduced as compared to that obtained with 250 mM NH4OH alone and this effect was accompanied by a significant rise in the GBF. This adaptive cytoprotection by 15 mM NH4OH was reversed, in part, by the pretreatment with indomethacin to inhibit prostaglandins (PG) or L-NAME to suppress nitric oxide (NO) formation or after capsaicin-induced denervation of sensory nerves. Blockade of endogenous sulfhydryls (SH) by N-ethylmaleimide (NEM) eliminated this adaptive cytoprotection but the suppression of ornithine decarboxylase (ODC), a key enzyme in polyamine biosynthesis, by alpha-difluoro methylornithine (DFMO) failed to influence the protection and accompanying hyperemia afforded by NH4OH in low concentration. The combination of urea (2%) and urease (100 U), which raised the gastric luminal NH4OH concentration by about 5-folds, also reduced significantly the lesions provoked by 250 mM NH4OH. This protection and accompanying hyperemia induced was significantly attenuated by the pretreatment with indomethacin or hydroxyurea, a potent urease inhibitor. Hydroxyurea abolished completely the rise in luminal NH4OH produced by the combined treatment of urea plus urease. We conclude that 1) NH4OH in high concentration damages the gastric mucosa but when applied at lower concentration or generated in the stomach by urea-urease system, acts as local mild irritant to induce adaptive cytoprotection that probably involves PG, sensory nerves and arginine-NO-pathaway.
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PMID:Urea-urease system in cytoprotection against acute mucosal damage. 877 94


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