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

The purpose of this investigation was to compare the antimicrobial properties of mouse urine and of urea against Escherichia coli and Proteus mirabilis. Nornal urine was found to inhibit the growth of E. coli and P. mirabilis, whereas urine from diuresing animals permitted multiplication of these bacteria. Addition of urea to urine from diuresing animals restored its bactericidal effect on P. mirabilis but not on E. coli. This bactericidal effect on P. mirabilis was dependent on the additive action of high content of urea and high pH and was prevented by the addition of urease inhibitor.
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PMID:Differential susceptibility of Escherichia coli and Proteus mirabilis to mouse urine and to urea. 1 46

A comparative study of properties of soluble urease and urease immobilized by its binding to cellulose derivatives was carried out. Upon chemical binding of urease to cellulose derivatives the Mikhaelis constant and pH optimum for the enzyme action changed insignificantly. Maximum enzymic activity of soluble and immobilized urease occurred at 50 degrees C. The energy of activation of urea hydrolysis by urease during enzyme immobilization also changed insignificantly.
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PMID:[Properties of urease immobilized by chemical binding to a derivatives of cellulose]. 2 Jun 17

The hydrolysis of urea by the bacterial enzyme urease pathologically increase urinary ammonia, bicarbonate, carconate and alkalinity. These factors contribute to the formation of urinary stones and to the virulence of bacteria. Acetohydroxamic acid, a potent inhibitor of urease, has been administered to 23 patients with staghorn renal calculi and urea-splitting urinary infection. Urinary ammonia and alkalinity has been reduced in every patient. A dose of 1.0 gm. acetohydroxamic acid daily has been well tolerated and effective for 2 to 12 months, even in patients with impaired renal function.
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PMID:Acetohydroxamic acid: clinical studies of a urease inhibitor in patients with staghorn renal calculi. 2 42

The yeast "H" of the genus Candida guilliermondii can grow on hydrocarbons as the only source for carbon. Urea can serve as a nitrogen source for this yeast which lacks detectable urease activity. During urea metabolism ammonia has never been accumulated in the culture medium. However, transferring the yeast from complete urea-medium into an urea containing phophate-buffer, the degradation of urea continues and ammonia is accumulated as well as CO2 evolved. In cell-free extracts of the yeast urea amidolyase activity was detected in the presence of ATP, biotin and specific cations. Obviously, the synthesis of urea amidolyase is induced by urea and arginine and repressed by the catabolite ammonia. Similarly the synthesis of arginase is regulated by arginine and ammonia. The analytical data of the arginase action differ significantly in relation to the carbon source of the culture medium. Both the level of arginase and ornithine carbamyl-transferase change in a characteristic way during the batch-culture. From the lower level of arginase in relation to ornithine carbamyltransferase it can be concluded that especially in alkane-metabolizing yeast the arginine catabolism is not very intensive.
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PMID:[Anabolic and catabolic enzymes of urea metabolism in a carbohydrate-utilizing strain of Candida guilliermondii]. 2 24

A novel, closed-loop drug delivery system was developed where the presence or absence of an external compound controls drug delivery from a bioerodible polymer. In the described delivery system, hydrocortisone was incorporated into a n-hexyl half-ester of a methyl vinyl ehter-maleic anhydride copolymer, and the polymer-drug mixture was fabricated into disks. These disks were then coated with a hydrogel containing immobilized urease. In a medium of constant pH and in the absence of external urea, the hydrocortisone release was that normally expected for that polymer at the given pH. With external urea, ammonium bicarbonate and ammonium hydroxide were generated within the hydrogel, which accelerated polymer erosion and drug release. The drug delivery rate increase was proportional to the amount of external urea and was reversible; that is, when external urea was removed, the drug release rate gradually returned to its original value.
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PMID:Controlled drug release by polymer dissolution. II: Enzyme-mediated delivery device. 3 27

Experiments and appropriate mathematical models are presented in an attempt to elucidate and separate the effects of mass transfer and immobilization on the apparent kinetics of hydrolysis of urea by urease immobilized within a crosslinked gelatin film. Diffusion of urea through the gelatin matrix appears to exert the major influence on the observed kinetics. Diffusion coefficients are measured, and a model for the "effectiveness factor" is presented, accounting for this aspect of mass transfer control. A secondary, but significant, influence on apparent kinetics arises because the reaction products lead to an increased pH level which, because of diffusion resistance, remains high within the gelatin matrix. For pH levels in the 6.7 to 9.0 range the activity of urease is a strongly decreasing function of pH. An approximate model accounting for ionic equilibrium allows this pH-diffusion effect to be introduced in such a way as to lead to predictions of the apparent kinetics that are compared with experimental observations. Examination of these results indicates that the immobilization procedure leads to some loss of activity due to an interaction of the gelatin crosslinking reaction with the enzyme itself.
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PMID:Hydrolysis of urea by gelatin-immobilized urease: separation of kinetic and diffusion phenomena in a model immobilized-enzyme reactor system. 4 51

The growth and utilization of nitrogen by intensive Chlorella vulgaris in wastes from production of urea, containing 1300 mg NH4+-N and 4000 mg urea-N/1, was investigated. In these conditions only Chlorella vulgaris AA strain, adapted to high concentrations of ammonia nitrogen, was able to grow. The elimination of nitrogen by continuous cultures was 750 mg urea-N/1 with 5-day flow rate. A considerable part of the urea was hydrolized by urease bacteria and removed in the form of NH3. The effect of intermittent light on the growth of algae was also studied. The better growth than in continuous light, was obtained with alternate one hour periods of light and darkness. Good results were also obtained with the use of 12 hour light and 12 hour darkness.
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PMID:Studies on the purification of wastes from the nitrogen fertilizer industry by intensive algal cultures. IV. growth of Chlorella vulgaris in wastes with high nitrogen content in continuous and intermittent light. 6 57

The catabolic products of arginine metabolism were observed in Aphanocapsa 6308, a unicellular cyanobacterium, by thin layer chromatography of growth media, by limiting growth conditions, and by enzymatic analysis. Of the organic, nitrogenous compounds examined, only arginine supported growth in CO2-free media. The excretion of ornithine at a concentration level greater than citrulline suggested the existence in Aphanocapsa 6308 of the arginine dihydrolase pathway which produced ornithine, CO2,NH4,+ adenosine 5'-triphosphate. Its existence was confirmed by enzymatic analysis. Although cells could not grow on urea as a sole carbon source a very active urease and subsequently an arginase were also demonstrated, indicating that Aphanocapsa can metabolize arginine via the arginase pathway. The level of enzymes for both pathways indicates a lack of genetic control. It is suggested that the arginase pathway provides only nitrogen for the cells wheras the arginine dihydrolase pathway provides not only nitrogen, but also CO2 and adenosine 5'-triphosphate.
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PMID:Arginine catabolism in Aphanocapsa 6308. 10 70

Strains of purple sulfur bacteria (Chromatium minutissimum, Ectothiorhodospira shaposhnikovii, Thiocapsa roseopersicina, Lamprobacter modestohalophilus) and nonsulfur bacteria (Rhodopseudomonas palustris, Rh. spheroides, Rhodospirillum rubrum) grow in media containing urea as a source of nitrogen at concentrations from 0.5 to 5.0%. They can also utilize the carbon of urea and thus grow in the absence of bicarbonate. Urea is decomposed by all the studied purple bacteria with the participation of urease. In a number of strains, the enzyme is inducible and is synthesized only in the presence of urea. However, it is constitutive in certain purple bacteria (L. modestohalophilus, Rh. palustris, Rh. spheroides). The strains of purple bacteria differ in the activity of urease and in its susceptibility to ammonium ions.
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PMID:[Use of urea by purple bacteria]. 11 59


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