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PubMedDate not supplied

[The influence of anodizing conditions on the activity of urease immobilized to anodized sheet aluminium (author's transl)].

The activity of urease immobilized by adsorption on anodized sheet aluminium strongly depends on the method chosen for preparation of these carriers. If oxalic acid is applied as electrolyte, only the anodizing temperature significantly influences the activity of the preparations. In case of the well-known GS process, however, the activity is not only affected by the temperature, but also by other conditions of anodizing, for example the current density and the electrolyte concentration. For both methods the correlation between the topography of the carrier surfaces and the activity of enzyme immobilized to the surface is described.

Aluminum↗
PubMed1995

Evaluation of a new urease reagent strip for detection of Helicobacter pylori in gastric biopsy specimens.

OBJECTIVES: Determine sensitivity and specificity of a new urease reagent strip (URS) test for detection of Helicobacter pylori in gastric biopsy specimens. METHODS: Six paired biopsy specimens were obtained from the greater curvature of the distal antrum, the lesser curvature near the incisura, and the corpus along the greater curvature during 66 procedures on 59 patients with endoscopic findings of gastric antral mucosal erythema or erosions, or gastric or duodenal ulcers. One biopsy from each site was tested with the URS. The second was evaluated with histology. A final antral biopsy was evaluated with a urea/gel test. RESULTS: Twenty-eight of the 66 cases were histologically positive, with H. pylori observed in at least one of the three biopsy sites. The URS test correctly identified all 28. Of 193 individual biopsy specimens, 78 were positive for H. pylori. The URS correctly identified 77. Sensitivity was 0.99, specificity 0.95, positive predictive value 0.93, negative predictive value 0.99, and kappa 0.92. Average time to positive was 20 min. Twenty-seven antral biopsies were histologically positive for H. pylori. The URS test correctly identified all 27, whereas the urea/gel test correctly identified 21. For antral sites, URS sensitivity was 1.00 and specificity 0.95 versus urea/gel test sensitivity of 0.75 and specificity of 1.00. CONCLUSIONS: In this sample, the URS test is as accurate as histology in diagnosing H. pylori infections, and it provides results in less time and at a lower cost than histology.

Bacteriological Techniques↗
PubMed1993

[Detection of Helicobacter pylori by the urease test in 244 patients].

The authors report the results of the detection of Helicobacter Pylori (HP) in gastric mucosa by the urease test, in 244 patients between January 1989 and August 1991. The overall prevalence of HP was 38.1%. It was 19.5% in patients with normal upper gastrointestinal endoscopy (UE), 61% in duodenal ulcer (p < 0.001) and 68.7% in congestive antritis (p < 0.001), significantly higher than in controls. There was no significant difference between controls and patients with erosive antritis or healed duodenal ulcers. The prevalence of HP rises with age in all patients and in those with lesions at UE but not in those with normal UE. A rise of this prevalence seems to exist in the months of June and December. The authors conclude by pointing out the rise of the overall prevalence of HP in congestive antritis compared with erosive antritis, the similarity of prevalence in normal subjects and those with healed ulcer and the lack of influence of age on this prevalence in subjects with normal UE. These conclusions are in need of confirmation by further studies on much more longer series.

Adolescent↗
PubMed1993

A strain of urease negative Cryptococcus neoformans isolated from the environment in China.

This is the first report of a strain of urease negative Cryptococcus neoformans isolated from the environment in China. The colonies of this isolate showed brown pigmentation on cornmeal agar with 300 micrograms/ml caffeic acid, but failed to hydrolyze urea. Microbiological identification and pathogenicity tests in mice confirmed this as a strain of C. neoformans. A similar strain had reportedly been isolated from an AIDS patient.

Animals↗
PubMed1993

Cryptococcosis produced by a urease negative strain of Cryptococcus neoformans.

A urease negative strain of Cryptococcus neoformans was isolated form a patient with AIDS. The identification of the yeast was confirmed by physiological and pathogenicity tests. Clinically, the disseminated cryptococcal infection in our patient was identical to those reported in other patients with AIDS.

AIDS-Related Opportunistic Infections↗
PubMed1977

[Inhibition of urease by hypoglycaemic drugs (author's transl)].

The effect of oral hypoglycaemic drugs (derived from sulphonylurea) on urease activity in the quantitative determination of urea has been studied. These compounds have been found to produce a competitive inhibition of enzyme activity with respect to substrate. Possible interference of these antidiabetic agents upon urea analysis is discussed.

Chlorpropamide↗
PubMed1975

Aerobacter aerogenes PRL-R3 urease. Purification and properties.

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.

Electrophoresis, Disc↗
PubMed1997

An evolutionary treasure: unification of a broad set of amidohydrolases related to urease.

The recent determination of the three-dimensional structure of urease revealed striking similarities of enzyme architecture to adenosine deaminase and phosphotriesterase, evidence of a distant evolutionary relationship that had gone undetected by one-dimensional sequence comparisons. Here, based on an analysis of conservation patterns in three dimensions, we report the discovery of the same active-site architecture in an even larger set of enzymes involved primarily in nucleotide metabolism. As a consequence, we predict the three-dimensional fold and details of the active site architecture for dihydroorotases, allantoinases, hydantoinases, AMP-, adenine and cytosine deaminases, imidazolonepropionase, aryldialkylphosphatase, chlorohydrolases, formylmethanofuran dehydrogenases, and proteins involved in animal neuronal development. Two member families are common to archaea, eubacteria, and eukaryota. Thirteen other functions supported by the same structural motif and conserved chemical mechanism apparently represent later adaptations for different substrate specificities in different cellular contexts.

Amidohydrolases↗
PubMed1997

Comparison of agar gel (CLOtest) or reagent strip (PyloriTek) rapid urease tests for detection of Helicobacter pylori infection.

OBJECTIVE: Rapid urease tests (RUTs) are used commonly as a convenient method to detect Helicobacter pylori infection. New rapid tests have been commercially available with promotional literature suggesting enhanced utility. We compared CLOtest to a new reagent strip RUT, PyloriTek. METHODS: Gastric antral mucosal biopsy specimens were obtained from 102 patients for comparison between CLOtest and PyloriTek (204 specimens). Biopsy specimens obtained from a nearby area were stained using the Genta stain for determination of H. pylori status. The RUT to be used first was selected randomly. RESULTS: Sixty-five of the 102 patients had peptic ulcer disease, two had gastric cancer, and 35 had dyspepsia; 61 patients had active H. pylori infection. There were one false-negative and three false-positive CLOtest results, compared with one false-negative and 13 false-positive PyloriTek results (p < 0.02 for incorrect categorization with PyloriTek). Sensitivity and specificity were 98 and 92% compared with 98 and 68% for CLOtest and PyloriTek, respectively. An erroneous categorization of H. pylori status occurred in 3.9% (95% confidence interval [CI]: 1-9.7%) with CLOtest compared with 13.7% (95% CI: 7.7 -22%) with PyloriTek. When the PyloriTek was scored at 1 h (0-1 h) after obtaining the specimen, the accuracy improved; erroneous categorization of H. pylori status occurred in only 2.9% (95% CI: 0.6-8.3%). CONCLUSION: Used according to manufacturer instructions, the new reagent strip RUT PyloriTek has too many false-positive results for use in a clinical situation. In contrast, when the test was interpreted within 1 h, accuracy was comparable to that of CLOtest.

Adult↗
PubMed1997

Kinetic assay of serum and urine for urea with use of urease and leucine dehydrogenase.

We describe a new kinetic assay for determining urea in serum or urine with use of urease (EC 3.5.1.5) and leucine dehydrogenase (EC 1.4.1.9). The latter enzyme is suitable for the kinetic assay of NH4+ because its Km value for NH4+ at pH 8.75 is large (approximately 500 mmol/L). Interference from endogenous NH4+ in serum or urine is obviated by subtraction of the assayed endogenous NH4+ value in a sample blank. For serum, within-assay CVs (n = 10) were 0.39-0.58%; day-to-day CVs (n = 10) were 1.56-2.30%. In urine, within-assay CVs (n = 10) were 0.86-1.15%. Analytical recovery of urea (0.893-71.4 mmol/L) added to patients' sera (urea 6.14 mmol/L) was 99.2-105.2%. The calibration curve for serum was linear through zero for urea concentrations up to 142.9 mmol/L and for urine up to 714.3 mmol/L. No influences of added ammonium ion, bilirubin, hemoglobin, ascorbic acid, or Intralipid were observed. The regression equations for this method (y) and conventional methods (x = Determiner-LUN for serum assays, Serotec UUR-R for urine) were: y = 1.016x - 0.12 mmol/L (r = 0.999, S(y/x) = 0.34 mmol/L, n = 100) for sera, and y = 1.070x - 12.6 mmol/L (r = 0.998, S(y/x) = 7.41 mmol/L, n = 100) for urine.

Amino Acid Oxidoreductases↗
PubMedDate not supplied

[Urinary urease activity in urolithiasis patients].

Urease activity (UA) and the ability of the urine to form crystals (AFC) were assessed in the urine from 149 urolithiasis patients and 11 healthy controls. Patients with primary uroliths had high UA and AFC in 17-18% of the cases, in recurrent urolithiasis this percentage was 29-35%. The speed of phosphate and oxalate crystals formation as well as formation of renal calculus correlated with UA and UA levels. Thus, UA and AFC may be employed as criteria in prognostication of the duration of phosphate and oxalate lithogenesis.

Crystallization↗
PubMed1997

Storage temperature of the unbuffered rapid urease test.

OBJECTIVES: The unbuffered rapid urease test (RUT) is an accurate, rapid, and inexpensive method for detecting Helicobacter pylori. However, it is generally recommended that the reagent be prepared daily. This prospective study was undertaken to evaluate the shelf life of our unbuffered RUT when stored at 4 and -20 degrees C. METHODS: Ninety-five patients were studied. Three sets of antral (X2) and body (X1) biopsy samples were taken from each patient. The samples were subjected to histological examination, with the RUTs stored at 4 and -20 degrees C. The RUT tubes were examined at 1 and 15 min. RESULTS: Fifty-six patients (59%) were infected with H. pylori as defined by histological examination. The reagent was classified according to storage time (group I, < or = 5 days; group II, > 5 days). The mean (SD) storage time of group I (n = 59) and group II (n = 36) was 3.2 (1.4) and 9.9 (5.0) days, respectively. At 15 min, the sensitivity of our RUT stored at 4 degrees C was significantly higher in group I than in group II (92 vs 47%). On the other hand, the sensitivity of our RUT stored at -20 degrees C remained consistently high in both groups (15 min: group I, 92%; group II, 100%). Our RUTs stored at 4 and -20 degrees C were highly specific in both groups. CONCLUSIONS: Our RUT remains highly sensitive and specific when it is stored at 4 degrees C for up to 5 days. When the RUT is expected to be stored for a longer period of time, the bottles should be frozen at -20 degrees C.

Biopsy↗
PubMed1987

Determination of the serological sex-specific (Sxs) antigen ("H-Y antigen") in birds and mammals using high-titer antisera and a sensitive urease ELISA.

A rapid, sensitive, and reproducible enzyme-linked immunosorbent assay (ELISA), for the detection of the serological sex-specific (Sxs) antigen (formerly termed H-Y antigen; see Introduction), is described. This assay uses bovine testes extract as the solid phase antigen, and high-titer anti-Sxs antisera and a urease-conjugated anti rat-IgG as the first and second antibody respectively. The urea containing substrate causes a pH shift in a positive reaction, which in turn is visualized by the use of bromocresol purple as a pH indicator. The method, and some representative applications of it, are described in detail.

Animals↗
PubMed2004

Urea potentiometric biosensor based on modified electrodes with urease immobilized on polyethylenimine films.

The development of a new electrochemical sensor consisting in a glass-sealed metal microelectrode coated by a polyethylenimine film is described. The use of polymers as the entrapping matrix for enzymes fulfils all the requirements expected for these materials without damaging the biological material. Since enzyme immobilization plays a fundamental role in the performance characteristics of enzymatic biosensors, we have tested four different protocols for enzyme immobilization to determine the most reliable one. Thus the characteristics of the potentiometric biosensors assembled were studied and compared and it appeared that the immobilization method leading to the most efficient biosensors was the one consisting in a physical adsorption followed by reticulation with dilute aqueous glutaraldehyde solutions. Indeed, the glutaraldehyde immobilized urease sensor provides many advantages, compared to the other types of sensors, since this type of urea biosensor exhibits short response times (15-30s), sigmoidal responses for the urea concentration working range from 1 x 10(-2.5) to 1 x 10(-1.5) M and a lifetime of 4 weeks.

Adsorption↗
PubMed2000

Significance of sulfhydryl groups in the activity of urease from pigeonpea (Cajanus cajan L.) seeds.

Titration of urease from pigeonpea (Cajanus cajan L.), a hexameric protein (mol. wt. 480000; subunit mol. wt. 80000), with 5,5'-dithiobis-(2-nitrobenzoate) (DTNB) reveals the presence of 5.82+/-0.13 'accessible' sulfhydryl groups per molecule of the enzyme protein (i.e. about one 'accessible' SH group per subunit). Denatured enzyme was found to titrate for 12.1+/-0.1 SH groups per molecule (i.e. about two SH groups per subunit). Half of the 'accessible' groups react faster than the remaining at pH 8.5 as well as pH 7.5. However, the reaction was slower at pH 7.5 than 8.5. Time-dependent loss of enzyme activity with DTNB was also found to be biphasic. The enzyme was inactivated at low concentration of p-chloromercuribenzoate (p-CMB), N-ethyl maleimide (NEM) and iodoacetamide. The inactivation reactions were biphasic, with half of the activity lost more rapidly than the remaining half. The loss of activity with p-CMB was linearly related to the blocking of accessible SH groups. Inactivation by p-CMB is largely reversible by addition of excess of cysteine. Fluoride ion strongly protects the enzyme against NEM inactivation, however, substrate urea provides much weaker protection against SH group reagents. The significance of these results is discussed.

Journal Article↗
PubMed2001

Urease-positive Trichophyton rubrum strains (previously described as T. raubitschekii): first isolations in Argentina.

The present study reports the first Argentinian human cases of tinea caused by urease-positive Trichophyton rubrum strains (corresponding to isolates previously described as T. raubitschekii) in order to supply geographical data for these strains that are very rarely isolated as agents of dermatophytosis. The two isolates were identified by morphological, cultural, and physiological characteristics. The strains were isolated from cases of tinea corporis and tinea unguium.

Adolescent↗
PubMed2005

Urea decomposition facilitated by a urease model complex: a theoretical investigation.

Density functional theory calculations were used to examine the role of the urease model complex [Ni2(bdptz)(micro-OH)(micro-H2O)(H2O)2](OTs)3(bdptz=1,4-bis(2,2'-dipyridylmethyl)-phthalazine; OTs=tosylate) in the degradation of urea. An elimination mechanism that converts urea to ammonium cyanate was investigated in detail. The lowest energy pathway involves urea coordination through the oxygen atom to a Ni center followed by protonation of a urea NH2 group by the bridging water ligand. Subsequent rotation of the protonated urea, followed by deprotonation of the NH2 by a bridging OH ligand generates the bound, disproportionated urea substrate, HNCONH3, from which ammonium cyanate was produced.

Journal Article↗
PubMed2001

Citric acid-enhanced Helicobacter pylori urease activity in vivo is unrelated to gastric emptying.

BACKGROUND: In a previous study, the use of a citric acid test meal produced a rapid dose-dependent increase in urease activity that was significantly greater than that resulting from a pudding meal, ascorbic acid or sodium citrate. The mechanism was hypothesized to be related to the ability of citric acid to delay gastric emptying and possibly to enhance intragastric distribution of the urea. OBJECTIVE: To compare the effects of sodium citrate, two doses of citric acid and a pudding meal on gastric motor function. METHOD: Eleven normal healthy volunteers were investigated using non-invasive techniques to measure gastric emptying and gastric motility. We evaluated gastric emptying using the Meretek 13Ceebiscuit solid phase gastric emptying breath test, which employs a 340-calorie biscuit containing 200 mg of the edible 13C-blue-green alga Spirulina platensis, after the administration of test meals of pudding, 2 g and 4 g of citric acid and 2 g of sodium citrate. Electrogastrograms (Digitrapper EGG) were also recorded for 30 min before and 180 min after the test meal. RESULTS: Gastric emptying, as assessed by the half-time (T1/2), was delayed similarly with the pudding (136.8 +/- 9 min) and with 4 g of citric acid (144.5 +/- 7 min) (P > 0.7). Sodium citrate (108.7 +/- 6 min) and 2 g of citric acid (110.1 +/- 6 min) had similar effects on gastric emptying (P=0.986), and were significantly less effective in delaying gastric emptying (P < 0.01) compared to pudding or 4 g of citric acid. The electrogastrograms remained normal and there were no differences among meals and no relation with the gastric emptying results. CONCLUSIONS: The increased intragastric urea hydrolysis associated with citric acid test meals cannot be attributed to delayed gastric emptying. Changes in the intragastric distribution of urea or a direct effect of citric acid on the bacteria (e.g. via the cytoplasmic protein, UreI) are more likely to be responsible.

Adolescent↗