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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)

A method for the preparation of a 150-fold purified and homogenous A. aerogenes urease is reported. The enzyme exhibited two pH optima at pH 7.0 and 7.5 in triethanolamine and phosphate buffer, respectively. The affinity of the enzyme toward its substrate increased with the increase of pH. No effect of the pH was observed on the measured temperature coefficient (Q10). There was no discontinuity in the Arrhenius plots at pH 5.4 and 7.5 but an upward discontinuity at pH 6.15 and 8.7 with transition temperature at 30 degrees C. Also, the calculated activation energies are greatly affected by the pH of the enzyme reaction mixture.
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PMID:Aerobacter aerogenes PRL-R3 urease. Purification and properties. 0 Aug 79

The urea-hydrolyzing activity of a T-strain mycoplasma was studied in experiments using whole cells and cell-free enzyme preparations by measuring the release of 14CO2 from [14C]urea. Under the conditions used, the urea concentration optimum is approximately 5.6 X 10(-3) M urea. The activity is soluble and not membrane bound. It is stable at -70 C for several weeks but is more labile at higher temperatures. The pH optimum is between 5.0 and 6.0. The effect of several inhibitors on the activity was tested and revealed similarities, as well as differences, between T-strain mycoplasma urease activity and the urease activity of other organisms and plants.
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PMID:Urea-hydrolyzing activity of a T-strain mycoplasma: Ureaplasma urealyticum. 0 81

Ornithine carbamyl transferase activity was determined by estimation of the citrulline formed during the reaction. Citrulline is estimated by diacetylmonoxime in the presence of thiosemicarbazide. The conditions of enzyme analysis were then studied in buffer veronal-acetate medium at 37 degrees C. The optimum pH for activity depended on the ornithine concentration, but was independent of carbamyl-phosphate concentration. At pH 7.8, ornithine at concentrations higher than 1.6 mM inhibited enzyme activity, ornithine Km was 0.208 mM and that of carbamyl-phosphate was 1.92 mM. The incubation time for determination of OCT activity was 15 minutes. Citrulline production was proportional to the enzyme concentration up to activities of 180 units/l. Serum urea was destroyed by a urease of high quality, so that the formation of citrulline in the control reagents was minimal. Reference values, determined on a hospital population, without liver, heart or pulmonary disease, lay between 4.7 +/- 2.3 units/l. The coefficient of variation of the technique, determined on a pool of serum of moderate activity was 8 units/l i.e. 5.1 per cent.
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PMID:[Determination of the activity of serum ornithine carbamoyltranferase : working conditions in a veronal-acetate medium]. 0 89

Sone strains of Klebsiella pneumoniae and K. oxytoca grown on nutrient agar may appear "urease negative" in a Ferguson type reagent medium after a 24 h incubation at 37 degrees C. Amongst such 147 so called urease negative strains, urease has been detected within a few hours in 79 strains, when bacteria have grown on media containing carbohydrates (Kligler iron agar, Drigalski lactose agar, SS agar and Worfel-Ferguson sucrose medium). Acid production by carbohydrate fermentation increases urease production by Klebsiella: pH 4 is the most convenient pH for urease synthesis by these bacteria. The other 68 strains have been considered as urease-less Klebsiella. The best results are obtained from culture on Worfel-Ferguson sucrose medium: urea hydrolysis is positive--on an average-after 1 hour and 30 minutes when detected in a Ferguson type reagent medium, and after 2 hours and 35 minutes when detected in a Christensen reagent medium.
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PMID:[Carbohydrate containing media for the detection of urease in "Klebsiella"]. 0 30

The use of methenamine in the treatment of urinary tract infections due to Proteus species is limited by urine alkalinity. Acetohydroxamic acid, an inhibitor of urease, maintains acidity despite growth of Proteus in urine. Easily achievable concentrations of acetohydroxamic acid in vitro systems that simulated the dynamics of the urinary tract potentiated the antibacterial effect of methenamine against Proteus species. The combined use of a urease inhibitor and methenamine may be effective in the treatment of urinary infection caused by these organisms.
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PMID:Further observations on the potentiation of the antibacterial effect of methenamine by acetohydroxamic acid. 0 73

(1) Urease (EC 3.5.1.5.) was modified with beta-1-[3,3-dimethyl-6'-nitrospiro-(indoline-2,2'-2H-benzopyrene)] propionic anhydride. Three amino acid residues of urease were modified by the anhydride at a molar ratio of 2000. (2) The activity of modified urease was decreased with ultraviolet irradiation and then restored to the initial activity with visible light irradiation. (3) Modified urease was used to prepare a urease-collagen membrane. The apparent Michaelis constant (Km) of the modified urease-collagen membrane ultraviolet light was identical to that of the membrane under visible light. (4) The optimum pH of the modified urease-collagen membrane was displaced toward lower pH values with ultraviolet irradiation. At higher ionic strength, the pH activity curve of the membrane was displaced toward higher pH values. (5) The thermostability of urease was increased with its modification.
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PMID:Photocontrol of urease-collagen membrane activity. 0 49

A mass fragmentographic method of high accuracy for determination of serum urea is described. A fixed amount of [15N2]urea is added to a fixed amount of serum, then the urea is converted into 5,5-diallyl barbituric acid by coupling with diallyl malonic acid diethyl ester. The barbiturate is then transferred from an alkaline water phase into an organic phase containing methyl iodine by ion-pair extraction using tetrabutyl ammonium as the positive counterion. The amount of urea is determined from the ratio between the recordings at m/e 236 and m/e 238 obtained after analysis with a combined gas chromatograph-mass spectrometer equipped with an MID-unit (multiple-ion detector). The two ions used correspond to the molecular peak in the mass spectrum of the methyl derivative of unlabeled and labeled 5,5-diallyl barbituric acid, respectively. The relative standard deviation of the method was 3.6%. A comparison between the mass fragmentographic method and a routine method for determination of serum urea based on the urease-Berthelot reaction gave a high correlation (r = 0.99) and a regression coefficient of 0.95.
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PMID:Determination of serum urea by mass fragmentography. 0 11

1. Collagen fibrils were modified with beta-1-[3,3-dimethyl-6'-nitrospiro-(indoline-2,2'-2H-benzopyran)] propionic anhydride. 2. Urease (urea amidohydrolase, EC 3.5.1.5) was immobilized in spiropyran collagen membrane. The activity of the urease-spiropyran collagen membrane was found to increase in the dark and then decrease with visible light irradiation. 3. The optimum pH of the urease-spiropyran collagen membrane under visible light was lowered in the dark. 4. The apparent Michaelis constant (K'm) of the urease-spiropyran collagen membrane in the dark was almost the same as that under visible light. The apparent maximum velocity was increased in the dark. 5. The diffusion coefficient of urea through the spiropyran collagen membrane in the dark was 1.4 times that under visible light. However, the increase of the diffusion rate was not responsible for the activity increase of the urease-spiropyran collagen membrane.
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PMID:Photocontrol of urease activity in spiropyran collagen membrane. 0 96

Tumor incidence was studied in 1,2-dimethylhydrazine (DMH) injected male rats assigned at weaning to isoenergetic casein-sucorse deits containing 7.5%, 15%, or 22.5% protein with or without 2.5% urea. Twenty rats fed each diet were given weekly intraperitoneal injections of DMH (15 mg/kg body weight/week) for the first 24 weeks and 20 were given saline. Of 96 DMH-injected rats necropsied after 28 weeks, 88 were necropsied during the 32nd or final week of the experiment. Adenocarcinomas of the small and large intestine were larger and significantly more numberous in rats fed 15% and 22.5% dietary protein. Keratin producing papillomas of the sebaceous glands of the external ear were observed first at 21 weeks in DMH-injected rats fed 22.5% protein. These were subsequently observed in some rats from all DMH-treated groups. As time progressed, the ear tumors increased in size and number in all groups but the greatest incidence was in the group fed 22.5% protein. No tumors were observed in saline-injected rats. Urea feeding did not increase the number of tumors nor cause changes in pH, urease activity or ammonia concentration of contents of the colon or cecum, or blood cholesterol. As dietary protein increased, cecal ammonia concentrations rose while both colon and cecal pH dropped. Portal blood urea and cholesterol reose as dietary protein was increased. DMH-treated rats had significantly higher concentrations of colon and cecal ammonia and lower blood cholesterol. Altough the rats fed 7.5% protein gained significantly less weight during 0 to 6 weeks of feeding, their weight gain was significantly higher during 6 to 26 weeks. No tumors were found in rats necropsied at 16 weeks.
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PMID:Nitrogen intake and tumorigenesis in rats injected with 1,2-dimethylhydrazine. 1 Mar 59

Meralluride, mercaptomerin, ethacrynic acid, and penicillamine inhibited urease activity of Proteus mirabilis. The activity of the organic mercurials and ethacrynic acid was markedly inhibited by human and dog urine. Antiurease activity could not be detected in the urine of a human and a dog given meralluride by injection. Urine from patients receiving penicillamine also failed to inhibit urease activity. Ascorbic acid inhibited, whereas dehydroascorbic acid enhanced, the activity of the mercurials, but neither agent altered the inhibitory effect of urine. The lethal effect of meralluride against Proteus occurred at the same concentration at which urease activity was inhibited, but penicillamine inhibited the enzymatic activity without affecting viability of the organism. The data suggest that these sulfhydryl-reactive compounds will not be useful against Proteus infections of the urinary tract.
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PMID:Effect of organic mercurials and sulfhydryl compounds on the urease activity of Proteus: inhibition by urine and ascorbic acid. 1 Aug 28


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