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PubMed1990

How variations in the composition of urine influence urease-induced crystallization.

To Study how the composition of urine influences urease-induced crystallization, human urine samples were incubated with urease and the subsequent precipitation measured. Beside the pH increase, the urinary content of magnesium and calcium had profound effects on the precipitation of magnesium ammonium phosphate and calcium phosphate, respectively. Urine phosphate, ammonium and osmolarity had no direct effects on the precipitation. Among the urine components with potential inhibitory properties, only albumin was found to be correlated with such an effect. This inhibitory activity was especially influential in urines with high calcium and magnesium levels. These findings suggest that the composition of urine could also influence the formation of stones consisting of magnesium ammonium phosphate and calcium phosphate.

Calcium Oxalate↗
PubMed1991

Studies of urease-induced crystallisation in undiluted human urine using the Coulter counter technique.

Urease-induced crystallisation was studied in different human urine samples after urease incubation. The studies were performed using the Coulter counter technique, which enables determination of the number and size of particles in a solution and calculation of the total particle volume. The crystallization took place in three consecutive but overlapping steps: (1) nucleation, (2) growth and (3) aggregation. The maximal number of particles obtained in the different samples varied little, but there was a great variation in particle size and total particle volume. The variation in particle size appeared to be mainly due to differences in particle growth, a factor that might be of importance for stone formation.

Adult↗
PubMed1981

Nitrogen control in Pseudomonas aeruginosa: a role for glutamine in the regulations of the synthesis of nadp-dependent glutamate dehydrogenase, urease and histidase.

In Pseudomonas aeruginosa the formation of urease, histidase and some other enzymes involved in nitrogen assimilation is repressed by ammonia in the growth medium. The key metabolite in this process appears to be glutamine or a product derived from it, since ammonia and glutamate did not repress urease and histidase synthesis in a mutant lacking glutamine synthetase activity when growth was limited for glutamine. The synthesis of these enzymes was repressed in cells growing in the presence of excess glutamine. High levels of glutamine were also required for the derepression of NADP-dependent glutamate dehydrogenase formation in the glutamine synthetase-negative mutant.

Ammonia↗
PubMed1986

Nickel-content of urease from Bacillus pasteurii.

Urease from Bacillus pasteurii DSM 33 was purified 34-fold to a maximum specific activity of 996.5 mumol urea min-1 mg-1 at 30 degrees C. Homogeneity was demonstrated by isoelectric focussing which showed a single protein zone corresponding to a pI of about 4.6. The native enzyme was demonstrated to have a molecular mass of 230,000 and to consist of identical subunits of 65,500, as measured by SDS electrophoresis. Radioactive 63Ni-nickel co-chromatographed with urease through gel filtration, ion-exchange, and affinity chromatography. Measuring specific radioactivity, the nickel content was found to be 1.00 (+/- 0.1) g-atom Ni per mol of subunit, and 0.82 g-atom Ni per mol as measured by atomic absorption spectrometry. This indicates that 1 atom of nickel is present in each of four subunits of the enzyme.

Bacillus↗
PubMed1996

A rapid urease test for presumptive identification of Cryptococcus neoformans.

A rapid method to evidence urease activity is described. Urea hydrolysis and consequent production ammonia are detected by a chemical reaction producing a blue phenol compound (indophenol blue). Three hundred and three yeast were tested. Out of 107 urease-positive organisms detected by Christensen's Urea Agar Test (CUAT) 102 were positive by our method. No false negatives were observed by this method when testing 87 Cryptococcus strains. Ths practical screening test for presumptive identification of Cryptococcus neoformans is simple, unaffected by pH changes and requires 15 minutes to be performed.

Clinical Laboratory Techniques↗
PubMed1991

On the false positive urease activity of Yarrowia lipolytica.

The ability of Yarrowia lipolytica to produce ammonia from urea was found variable on some media. The colour change of the indicator in Christensen's urea agar was not due to the urease activity of this species but was a non-specific alkalization reaction. Rapid urea broth was reliable giving no false positive results. It was found that Y. lipolytica is a urease negative yeast species.

Ammonia↗
PubMed1991

Ubiquinone and urease distribution in Taphrina and Symbiotaphrina.

Identifications of ubiquinone isoprenologues are presented for isolates identified with six species of Taphrina and for isolates of the two species of Symbiotaphrina. All had Q-10 as the major ubiquinone system. The inclusion of T. populina and S. buchneri, the respective type species, establishes this as the value for these genera. Both species of Symbiotaphrina were urease positive even though, according to the literature, they are unable to utilize urea as a sole nitrogen source. The urease results for the Taphrina isolates were mixed.

Ascomycota↗
PubMed1997

Urease-induced crystallizations of calcium phosphate and magnesium ammonium phosphate in synthetic urine and human urine.

An aggregometer technique was used to study urease-induced crystallizations in synthetic urine and human urine from healthy subjects and patients with chronic spinal cord injuries. The two different phases of crystallization, calcium phosphate and magnesium ammonium phosphate, were easily evaluated with a single assay using this technique. The crystallization of calcium phosphate and magnesium ammonium phosphate varied markedly among the different urine specimens after incubation with urease. The turbidity curves from human urine were divided into four patterns. We assumed that the variations in the patterns of the turbidity curves appeared to be mainly due to differences in the composition of the urine and in the original pH, and that the calcium and magnesium concentrations were very important in the urinary constituents.

Calcium Phosphates↗
PubMed1993

Citrate and urease-induced crystallization in synthetic and human urine.

The effects of citrate on the different phases of urease-induced crystallization were studied using Coulter counter techniques and optical microscopy. Citrate increased urine pH and markedly delayed the initiation of the crystallization (nucleation) in both human and synthetic urine. In synthetic urine, particle aggregation and especially particle growth were delayed and inhibited by citrate. In human urine, aggregation was distinctly inhibited by citrate. It appears that the susceptibility of urine to form crystals in the presence of urease activity is influenced by its citrate concentration.

Adult↗
PubMed1986

S.E.M. study of urease-induced crystalluria in the presence of hydroxamic derivatives.

The effect of 3 hydroxamic acid derivatives on urease-induced crystalluria was studied in vitro. Acetohydroxamic acid is more effective than salicylhydroxamic and gentisohydroxamic acids in inhibiting the kinetic of urease enzymatic reaction and in retarding the formation of struvite and apatite. Crystal deposits studied by scanning electron microscope (S.E.M.) and X-ray microanalysis indicated that acetohydroxamic acid favours the formation of large crystals of struvite, and less aggregation is observed. Salicyl and gentiso derivatives favour the formation of brushite together with struvite and apatite.

Apatites↗
PubMed2005

Effects of slow-release urea fertilizers on urease activity, microbial biomass, and nematode communities in an aquic brown soil.

A field experiment was carried out at the Shenyang Experimental Station of Ecology (CAS) in order to study the effects of slow-release urea fertilizers high polymer-coated urea (SRU1), SRU1 mixed with dicyandiamide DCD (SRU2), and SRU1 mixed with calcium carbide CaC2 (SRU3) on urease activity, microbial biomass C and N, and nematode communities in an aquic brown soil during the maize growth period. The results demonstrated that the application of slow-release urea fertilizers inhibits soil urease activity and increases the soil NH4+-N content. Soil available N increment could promote its immobilization by microorganisms. Determination of soil microbial biomass N indicated that a combined application of coated urea and nitrification inhibitors increased the soil active N pool. The population of predators/omnivores indicated that treatment with SRU2 could provide enough soil NH4+-N to promote maize growth and increased the food resource for the soil fauna compared with the other treatments.

Acetylene↗
PubMed2001

Structure-based computational study of the catalytic and inhibition mechanisms of urease.

The viability of different mechanisms of catalysis and inhibition of the nickel-containing enzyme urease was explored using the available high-resolution structures of the enzyme isolated from Bacillus pasteurii in the native form and inhibited with several substrates. The structures and charge distribution of urea, its catalytic transition state, and three enzyme inhibitors were calculated using ab initio and density functional theory methods. The DOCK program suite was employed to determine families of structures of urease complexes characterized by docking energy scores indicative of their relative stability according to steric and electrostatic criteria. Adjustment of the parameters used by DOCK, in order to account for the presence of the metal ion in the active site, resulted in the calculation of best energy structures for the nickel-bound inhibitors beta-mercaptoethanol, acetohydroxamic acid, and diamidophosphoric acid. These calculated structures are in good agreement with the experimentally determined structures, and provide hints on the reactivity and mobility of the inhibitors in the active site. The same docking protocol was applied to the substrate urea and its catalytic transition state, in order to shed light onto the possible catalytic steps occurring at the binuclear nickel active site. These calculations suggest that the most viable pathway for urea hydrolysis involve a nucleophilic attack by the bridging, and not the terminal, nickel-bound hydroxide onto a urea molecule, with active site residues playing important roles in orienting and activating the substrate, and stabilizing the catalytic transition state.

Algorithms↗
PubMed2000

The complex of Bacillus pasteurii urease with acetohydroxamate anion from X-ray data at 1.55 A resolution.

The structure of Bacillus pasteurii urease inhibited with acetohydroxamic acid was solved and refined anisotropically using synchrotron X-ray cryogenic diffraction data (1.55 A resolution, 99.5% completeness, data redundancy = 26, R-factor = 15.1%, PDB code 4UBP). The two Ni ions in the active site are separated by a distance of 3.53 A. The structure clearly shows the binding mode of the inhibitor anion, symmetrically bridging the two Ni ions in the active site through the hydroxamate oxygen and chelating one Ni ion through the carbonyl oxygen. The flexible flap flanking the active site cavity is in the open conformation. The possible implications of the results on structure-based molecular design of new urease inhibitors are discussed.

Anions↗
PubMed2001

Structure-based rationalization of urease inhibition by phosphate: novel insights into the enzyme mechanism.

The structure of Bacillus pasteurii urease (BPU) inhibited with phosphate was solved and refined using synchrotron X-ray diffraction data from a vitrified crystal (1.85 A resolution, 99.3% completeness, data redundancy 4.6, R-factor 17.3%, PDB code 6UBP). A distance of 3.5 A separates the two Ni ions in the active site. The binding mode of the inhibitor involves the formation of four coordination bonds with the two Ni ions: one phosphate oxygen atom symmetrically bridges the two metal ions (1.9-2.0 A), while two of the remaining phosphate oxygen atoms bind to the Ni atoms at 2.4 A. The fourth phosphate oxygen is directed into the active site channel. Analysis of the H-bonding network around the bound inhibitor indicates that phosphate is bound as the H2PO4- anion, and that an additional proton is present on the Odelta2 atom of Asp(alpha363), an active site residue involved in Ni coordination through Odelta1. The flexible flap flanking the active site cavity is in the open conformation. Analysis of the complex reveals why phosphate is a relatively weak inhibitor and why sulfate does not bind to the nickels in the active site. The implications of the results for the understanding of the urease catalytic mechanism are reviewed. A novel alternative for the proton donor is presented.

Bacillus↗
PubMed2004

Inhibition of soybean urease by triketone oximes.

Competitive inhibition of soybean urease by 15 triketone oximes has been studied at 36 degrees C in aqueous solution (pH 4.95). The studied oximes are supposed chelators for the nickel atom in the urease metallocenter. The inhibition constants of urea hydrolysis (K(i)) varied in the range 2.7-248 microM depending on the oxime structure. Analysis of this dependency demonstrates that the optimal inhibitor is the one containing carbonyl group in position 1 of the cycle, the ethoxyimino group and alkyl residue in the substituent in position 2, as well as the methoxycarbonyl group in position 4 of the cycle.

Enzyme Inhibitors↗
PubMed2005

Comparison of the clinical feasibility of three rapid urease tests in the diagnosis of Helicobacter pylori infection.

Rapid urease tests (RUTs) are a fast, accurate, and inexpensive method to diagnose H. pylori infection in the endoscopy suite. Of these, the CLO test is both common and widely used. The aim of our study was to evaluate the accuracy and positive reaction times of two new rapid urease tests (ProntoDry and HpONE) in comparison with the CLO test. Fifty-one patients (26 men, 25 women; mean age, 52.4 years) were included in this study, and all underwent esophagogastroduodenoscopy (EGD). None of the patients had received any prior H. pylori eradication therapy. H. pylori infection status was evaluated by histology, culture, 13C-UBT, and RUT. H. pylori infection was considered to be positive if the culture was positive or if two of the other three tests (histology, RUT, and 13C-UBT) were positive. If culture was negative and only one of the other three tests was positive, or if all four tests were negative, the result was interpreted as negative. Of these 51 patients, 2 were excluded and 29 (59.1%) were infected with H. pylori. The sensitivities, specificities, positive predictive values, and negative predictive values of the three RUTs were not significantly different. The mean positive reaction times of the three RUTs (CLO test, ProntoDry, and HpONE) were 67.8+/-12.0, 16.5+/-2.2, and 17.8+/-2.1 min, respectively. ProntoDry (P < 0.001) and HpONE (P < 0.001) had significantly faster reaction times than the CLO test, but there was no significant difference between ProntoDry and HpONE. Different media of RUTs may influence the rapidity of a positive reaction time. Both ProntoDry and HpONE were superior to the CLO test in terms of accuracy, reaction time, and cost-effectiveness.

Adult↗
PubMed2007

Quantifying gastric Helicobacter pylori infection: a comparison of quantitative culture, urease breath testing, and histology.

Although there are several methods to detect Helicobacter pylori infection, there is no simple validated test to quantify the density of infection, which is believed to play a major role in the pathogenesis of H. pylori-associated gastritis and peptic ulceration. The aim of this study was to evaluate and compare noninvasive and invasive tests for assessing the level of H. pylori infection so as to facilitate the development and clinical testing of new antibiotic treatments. Healthy volunteers (n=323) were screened for H. pylori infection by serology and, if positive (n=86), invited to undergo (13)C urea breath testing (UBT) (n=55). An increase of >2.4 parts per thousand (13)CO(2) at 15 min compared to baseline was considered a positive test. Total cumulative urease activity (mumol) at 60 min was also calculated. UBT-positive subjects underwent endoscopy and nine biopsies were obtained from defined sites for quantitative culture and histological grading using the modified Sydney System. A total of 19 subjects were studied, 4 of whom underwent repeat testing. All subjects were positive for H. pylori by serology, UBT, culture, and histology. The increase in (13)CO(2) at 30 min correlated with the total cumulative urease activity at 60 min (r (2)=0.92, P< 0.0001). Bacterial counts (log cfu/biopsy; mean+/-SD) were 3.9+/-0.5, 3.9+/-0.4, and 3.9+/-0.6 at the lesser curve antrum, greater curve antrum, and corpus, respectively. There was no significant correlation between UBT results and bacterial counts at any biopsy site. Nor was there any significant correlation between the histology grading and either the UBT or the bacterial counts at any site. This study indicates that there is little correlation among the three methods used to measure bacterial burden in H. pylori infection. Thus, decrements in bacterial numbers during single-agent therapy cannot be measured reliably by UBT and therefore cannot be used to evaluate the potential efficacy of novel agents to treat gastric H. pylori infection.

Adult↗