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)

A series of 99 consecutively operated patients presenting staghorn stones has been reviewed to ascertain the factors implicated in recurrent calculogenesis. 71.7% of the calculi were infection stones; 50.7% harbored Proteus species bacteria and 33.8% Escherichia coli. Struvite stones were found in 57.6% followed at long distance (18.2%) by carbonate apatite, calcium oxalate (11.1%) and mixed (9.1%) stones. Postoperative assessment revealed 17% residual stones, which enhanced infection in 46.7% of these cases and regrew to form a new dendritic stone in 33.3%; 80% of these repeat stones were struvite. 31.5% of the patients initially freed of their calculi by the operation, had true recurrences, and 56.5% of them had resistant urinary infection, caused by Proteus or E. coli (50%-50%). Progressive growth of the recurrent lithiasis occurred in 61.5% of the infected cases, while 87.5% of the recurrences occurring in patients with sterile urine remained stabilized. In the group of nonrecurring lithiasis (56.8%) only 16% had urinary infection. These results confirm the preponderant role played by infection in the pathogenesis of staghorn "malignant' lithiasis and move the authors to make a plea in favor of postoperative integrated therapy, including the use of long-term antibacterial agents and urease inhibitors.
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PMID:The problem of recurrences and infection after surgical removal of staghorn calculi. 703 22

Three strains of Succinivibrio dextrinosolvens isolated from the rumen of cattle or sheep under diverse conditions grew well in a minimal medium containing glucose, minerals, cysteine, methionine, leucine, serine, ammonia, 1,4-naphthoquinone, p-aminobenzoic acid, and bicarbonate-carbonic acid buffer, pH 6.7. When menadione or vitamin K5 was substituted for 1,4-naphthoquinone, the growth rate was somewhat depressed. Growth was poor with vitamin K1 and ammonia, further addition of the amino acids aspartic acid, arginine, histidine, and tryptophan was necessary for good growth of type strain 24, but the other two strains grew well only in media containing ammonia. Strains C18 and 22B produced urease and grew well when ammonia replaced urea. When urea replaced ammonia, strain 24 grew poorly and urease activity could not be detected. Strain 24 required no B-vitamins, but the other two strains were stimulated by p-aminobenzoic acid. The methionine requirement was not placed by vitamin B12, betaine, or homocysteine. Cysteine was replaced by sulfide in strain 24 but less well in the other two strains. Very poor growth was obtained when sulfate replaced cysteine. The half-saturation constant for ammonia during growth of S. dextrinosolvens is more than 500 microM, a much higher value than that of many rumen bacteria.
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PMID:1,4-Naphthoquinone and other nutrient requirements of Succinivibrio dextrinosolvens. 712 52

The strict dependence of struvite and carbonate apatite renal stones on the urease-producing germs confirm the need to combine bacterial urease inhibitor drugs with antibiotic treatment. Of the two antiurease drugs used the better results were obtained with acetohydroxamic acid, both for its minimum side effects and its more powerful urease-inhibitor capacity. Thus stone recurrence was avoided even in patients with urinary infection not responding to specific antibiotic treatment.
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PMID:Urease inhibitor therapy in infected renal stones. 725 Jan 61

The values of Km and V, pH optimum and thermal stability of urease were determined. It was shown that urease can be effectively used for the study of equilibrium of synthesis and hydrolysis of carbamide under conditions of carbamide in the ammonium carbonate--carbamide--water system at 20 degrees and 37 degrees were determined. The equilibrium constants for carbamide synthesis at the given temperatures were calculated.
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PMID:[Equilibrium of the reactions of synthesis and hydrolysis of carbamide in the presence of urease]. 738 69

Urease (urea amidohydrolase; EC 3.5.1.5) catalyzes the hydrolysis of urea to yield ammonia and carbamate. The latter compound spontaneously decomposes to yield another molecule of ammonia and carbonic acid. The urease phenotype is widely distributed across the bacterial kingdom, and the gene clusters encoding this enzyme have been cloned from numerous bacterial species. The complete nucleotide sequence, ranging from 5.15 to 6.45 kb, has been determined for five species including Bacillus sp. strain TB-90, Klebsiella aerogenes, Proteus mirabilis, Helicobacter pylori, and Yersinia enterocolitica. Sequences for selected genes have been determined for at least 10 other bacterial species and the jack bean enzyme. Urease synthesis can be nitrogen regulated, urea inducible, or constitutive. The crystal structure of the K. aerogenes enzyme has been determined. When combined with chemical modification studies, biophysical and spectroscopic analyses, site-directed mutagenesis results, and kinetic inhibition experiments, the structure provides important insight into the mechanism of catalysis. Synthesis of active enzyme requires incorporation of both carbon dioxide and nickel ions into the protein. Accessory genes have been shown to be required for activation of urease apoprotein, and roles for the accessory proteins in metallocenter assembly have been proposed. Urease is central to the virulence of P. mirabilis and H. pylori. Urea hydrolysis by P. mirabilis in the urinary tract leads directly to urolithiasis (stone formation) and contributes to the development of acute pyelonephritis. The urease of H. pylori is necessary for colonization of the gastric mucosa in experimental animal models of gastritis and serves as the major antigen and diagnostic marker for gastritis and peptic ulcer disease in humans. In addition, the urease of Y. enterocolitica has been implicated as an arthritogenic factor in the development of infection-induced reactive arthritis. The significant progress in our understanding of the molecular biology of microbial ureases is reviewed.
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PMID:Molecular biology of microbial ureases. 756 14

Struvite renal stones are caused by infection of the urine with bacteria that synthesize the enzyme urease. Ammonium is released by the breakdown of urea by urease, the urine becomes highly alkaline, and magnesium ammonium phosphate (struvite) and carbonate apatite crystallize. Incorporation of the infecting bacteria within the developing stone, results in a focus of infection that is resistant to conventional antimicrobial therapy, and which is manifested clinically by repeated urinary tract infection caused by persistent bacteriuria. Extracorporeal shock wave lithotripsy (ESWL) currently is accepted as the election treatment for most renal calculi. This trial examines the bacteriologic aspects pre and post-ESWL. Eighty adult patients, 47 females and 33 males, without clinical signs of urinary tract infections (UTI) were submitted to urine cultures pre and post-ESWL. The first 50 patients underwent during and post-ESWL, 150 blood cultures, which all proved to be negative, confirming very low risk of generalized sepsis. No patient presented fever, chills or rigors pre or postprocedures. With respect to urine cultures 43 patients (52.5%) had a pre-ESWL UTI, in comparison to 49 (60%) who had a UTI post-ESWL. The distribution of organisms pre and post-ESWL was as follows: Proteus mirabilis (22/22), Escherichia coli (11/11), Pseudomonas aeruginosa (4/5), Klebsiella pneumoniae (2/2), Enterobacter cloacae (0/1), Alcaligenes odorans (1/2) Enterococcus faecalis (1/3), Staphylococcus saprophyticus (1/2) and Candida albicans (1/1). In this study 6 patients presented bacteriuria post-ESWL probably due to bacteria from inside the calculi. According to these results, the risk of bacteremia seems to be very low. In 60% of staghorn renal stones we could demonstrate a bacterial infection.
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PMID:[Staghorn renal lithiasis treated with shock waves. Bacteriologic aspects]. 765 75

A membrane reactor-separator, in which an anion-exchange membrane and a urease-immobilized poly(vinyl alcohol) (PVA) membrane were clamped together to separate the feed solution and the stripping solution of a dialysis cell, was constructed. The urea in the feed solution passed through the anion-exchange membrane, water film, and then was hydrolyzed to ammonium carbamate in the urease-immobilized PVA membrane. The experimental results showed that no ammonium ion was found in the feed solution under either phosphate or citrate buffer systems at 0.05-0.2 mol dm-3 and pH 6-9, and various initial concentrations of urea in the feed solution (20-200 mmol dm-3). This indicates that the water film between two membranes allows the carbamate ions to decompose into ammonium and carbonate ions completely before entering the anion-exchange membrane. The device therefore can be used for the removal of urea from feed solution, while preventing the backflow of ammonium ions from the stripping solution or water film into feed solution. It has significant potential in the development of a wearable or portable artificial kidney. The properties of the urease-immobilized PVA membrane were examined. A kinetic model describing the transport-reaction behavior of urea in the membrane reactor-separator was developed, and the optimum values of the reactor parameters were obtained.
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PMID:Transport and hydrolysis of urea in a reactor-separator combining an anion-exchange membrane and immobilized urease. 776 2

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

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

We developed a new urea sensor for the on-line monitoring of hemodialysis adequacy. The biosensor consisted of an immobilized urease cartridge placed between magnetoinductive conductivity cells. The biosensor output was taken as the conductivity difference between these cells. The device was placed on the ultrafiltrate line of a paired filtration dialysis system. The amount of urease present in the cartridge was sufficient for the complete conversion to ammonium carbonate of urea up to 35 mmol/L. Agreement was good between the urea concentration by the biosensor method and an automated analyzer for seven patients: range 8.07-30.3 mmol/L (22.6-84.8 mg/dL blood urea nitrogen, BUN); intercept 0.20 +/- 0.1 mmol/L (0.55 +/- 0.4 mg/dL BUN); slope 1.01 +/- 0.01; r 0.997; S(y/x) 0.40 mmol/L (1.11 mg/dL BUN). The device proposed meets the requirements of accuracy, cost, ruggedness, and ease of use (no calibration required) for a biosensor to be used for continuous monitoring of hemodialysis.
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PMID:Robust, reliable biosensor for continuous monitoring of urea during dialysis. 867 92


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