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)

Texel wethers (68 +/- 2.5 kg BW) fitted with catheters in the ruminal veins and a mesenteric artery, blood flow probes on ruminal arteries, and a ruminal cannula were fed 500 g of orchardgrass hay every 12 h. During the last third of the feeding cycle, intraruminal injections were performed to evaluate the effect of urease activity, osmolality, and concentrations of NH3, butyrate, and CO2 in the rumen on urea and NH3 fluxes across the rumen wall. At pH 6.7, NH3 absorption increased with NH3 and butyrate concentrations in the rumen, and to a lesser extent with CO2 concentration. The increase in ruminal blood flow associated with CO2 and butyrate increase was always greater than the increase in NH3 absorption. Increasing ruminal osmolality slightly decreased NH3 absorption. Ruminal NH3 concentration and ruminal blood flow seemed to be the main determinant of NH3 absorption. Decreasing urease activity in the rumen decreased urea net transfer. The net transfer of urea to the rumen was stimulated by CO2. High concentrations of NH3 (330 mg of N/L) and butyrate (25 mM) in the rumen decreased urea net uptake, whereas osmolality (up to 420 mOsmol/L) did not affect it. Modifications in ruminal blood flow or water net movement across the ruminal wall did not seem to account for the effect of CO2, NH3, and butyrate on urea net uptake.
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PMID:Net transfer of urea and ammonia across the ruminal wall of sheep. 822 81

The in vitro effect of urea and hydrolysis of urea by urease on mucus H+ permeability is reported here. The effective DHCl values indicate a strong pH dependence for H+ diffusion in both water and mucus layers, with no apparent trend at concentrations between 1 and 50 mM urea. However, the estimated DHCl at near-neutral and alkaline pH are 4- to 10-fold lower through mucus than through aqueous films. Moreover, the pKa values of HCO3- and NH3 (generated by urease action on urea) had a profound effect on measured DHCl. These in vitro studies suggest that a high local concentration of NH3 and HCO3- within the mucus layer, generated by the action of Helicobacter pylori urease on endogenous intragastric urea, could greatly accelerate proton flux to the surface epithelium by operation of a buffer shuttle. This results in enhanced H+ permeability, particularly at pKa values of HCO3- and NH3, and in extreme circumstances it may result in gastric ulcer formation.
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PMID:An in vitro study of enhanced H+ diffusion by urease action on urea. Implications for Helicobacter pylori-associated peptic ulceration. 826 22

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

A two-step method for assaying creatinine in serum and urine samples, suitable with automated analyzers, is reported. Reagent 1, for the first step, contains a blanking system [creatine amidinohydrolase (CRTase), urease, glutamate dehydrogenase, NADPH, and 2-oxoglutarate] and a NADPH-regenerating system [Mg(2+)-dependent isocitrate dehydrogenase (ICD), MgCl2, and excess isocitrate]. Reagent 2, for the second step, contains the metal-chelating reagent trans-1,2-cyclohexanediamine-N,N,N',N'-tetraacetic acid (CyDTA) and a trigger system [creatinine amidohydrolase (CRNase)]. When a specimen is mixed with reagent 1, all the creatine, urea, and NH3 present are removed by the blanking and NADPH systems. On adding reagent 2, CyDTA inactivates ICD to inhibit the NADPH system. Simultaneously, the creatinine (1 mol) in the specimen is hydrolyzed into creatine by CRNase, and then releases NADP+ (2 mol) through the blanking system. Our optimized method can determine creatinine linearly up to 500 mg/L, with within-day CVs < 1.2% and day-to-day CVs < 2.7%.
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PMID:Enzymatic rate assay of creatinine in serum and urine. 840 98

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

In Klebsiella aerogenes, the formation of a large number of enzymes responds to the quality and quantity of the nitrogen source provided in the growth medium, and this regulation requires the action of the nitrogen regulatory (NTR) system in every case known. Nitrogen regulation of several operons requires not only the NTR system, but also NAC, the product of the nac gene, raising the question of whether the role of NAC is to activate operons directly or by modifying the specificity of the NTR system. We isolated an insertion of the transposon Tn5tac1 which puts nac gene expression under the control of the IPTG-inducible tac promoter rather than the nitrogen-responsive nac promoter. When IPTG was present, cells carrying the tac-nac fusion activated NAC-dependent operons and repressed NAC-repressible operons independent of the nitrogen supply and even in the absence of an active NTR system. Thus, NAC is sufficient to regulate operons like hut (encoding histidase) and gdh (encoding glutamate dehydrogenase), confirming the model that the NTR system activates nac expression and NAC activates hut and represses gdh. Activation of urease formation occurred at a lower level of NAC than that required for glutamate dehydrogenase repression, and activation of histidase formation required still more NAC.
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PMID:The product of the Klebsiella aerogenes nac (nitrogen assimilation control) gene is sufficient for activation of the hut operons and repression of the gdh operon. 845 54

Proteus mirabilis urease, a nickel-containing enzyme, has been established as a critical virulence determinant in urinary tract infection. An amino acid sequence (residues 308 to 327: TVDEHLDMLMVCHHLDPSIP) within the large urease subunit, UreC, is highly conserved for every urease examined thus far and has been suggested to reside within the enzyme active site. Histidine residues have been postulated to play a role in catalysis by coordinating Ni2+ ions. To test this hypothesis, oligonucleotide-directed mutagenesis was used to change amino acid His-320 to Leu-320 within UreC. The base change (CAT for His-320 to CTT for Leu-320) was confirmed by DNA sequencing. The recombinant and mutant proteins were expressed at similar levels in Escherichia coli as detected by Western blotting (immunoblotting) of denaturing and nondenaturing gels. Specific activities of the enzymes were quantitated after partial purification. Strains expressing the mutant enzyme showed no detectable activity, whereas strains expressing the recombinant enzyme hydrolyzed urea at 149 mumol of NH3 per min per mg of protein. In addition, the mutant enzyme was able to incorporate only about one-half (58%) of the amount of 63Ni2+ incorporated by the active recombinant enzyme. While the mutation of His-320 to Leu-320 within UreC does not affect expression or assembly of urease polypeptide subunits UreA, UreB, and UreC His-320 of UreC is required for urea hydrolysis and proper incorporation of Ni2+ into apoenzyme.
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PMID:Proteus mirabilis urease: histidine 320 of UreC is essential for urea hydrolysis and nickel ion binding within the native enzyme. 850 Aug 94

The in vitro effect of ammonium bicarbonate buffer on mucus H+ permeability is reported here. The diffusional resistance of mucus and water was demonstrated to be dependent on buffer concentration, and the contrast between the two types of layers was most pronounced for low buffer concentration near neutrality. Moreover, the pKa values of HCO3- and NH3 had a profound effect on measured DHCl. These in vitro studies suggest that a potentially damaging high local concentration of NH3 and HCO3- within the mucus layer generated by the action of Helicobacter pylori urease on endogenous intragastric urea could greatly accelerate proton flux to the surface epithelium by operation of a buffer shuttle. This results in enhanced H+ permeability, particularly at pKa values of HCO3- and NH3, and that in extreme circumstances this may result in gastric ulcer formation.
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PMID:Enhanced H+ diffusion by NH4+/HCO3-: implications for Helicobacter-pylori-associated peptic ulceration. 851 85

Helicobacter pylori, an etiologic agent of gastritis and peptic ulceration in humans, synthesizes urease, a nickel metalloenzyme, as its most abundant protein. NixA, a high-affinity nickel transport protein, allows synthesis of catalytically active urease when coexpressed with H. pylori urease in an Escherichia coli host. To determine whether NixA is essential for the production of active urease in H. pylori, nixA was insertionally inactivated with a kanamycin resistance cassette (aphA) and this construct was electroporated into H. pylori ATCC 43504; allelic exchange mutants were selected on kanamycin-containing medium. The nixA mutation, confirmed by PCR, reduced urease activity by 42% (140 +/- 70 micromol of NH3/min/mg of protein in the mutant versus 240 +/- 100 micromol of NH3/min/mg of protein in the parent (P = 0.037). Rates of nickel transport were dramatically reduced (P = 0.0002) in the nixA mutant (9.3 +/- 3.7 pmol of Ni2+/min/10(8) bacteria) of H. pylori as compared with the parent strain (30.2 +/- 8.1 pmol of Ni2+/min/10(8) bacteria). We conclude that NixA is an important mediator of nickel transport in H. pylori. That residual nickel transport and urease activity remain in the nixA mutant, however, provides evidence for the presence of a redundant transport system in this species.
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PMID:Allelic exchange mutagenesis of nixA in Helicobacter pylori results in reduced nickel transport and urease activity. 869 29

Urease (E.C 3.5.1.5) was covalently immobilized on activated methoxypolyethyleneglycol-5000 which is linear, uncharged, soluble in water and nonimmunogenic. mPEG is bound to the epsilon-NH2 groups of Lysin in urease. Previously different molar ratios of urease -Lys/activated-mPEG were searched for immobilization. Storage stabilities, molecular weights and the values of blocked amino groups were determined for each immobilized urease and the best conditions was found 1:3 urease-Lys/activated mPEG. Furthermore physical characterization, kinetic constants (Km, Vmax), heat and temperature stabilites were also determined.
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PMID:Immobilization of urease on activated methoxypolyethyleneglycol-5000. 877 43


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