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At least 1,009 records · Page 56Linked to original sources
PubMed1994

The evolutionarily conserved ribosomal protein L23 and the cationic urease beta-subunit of Yersinia enterocolitica O:3 belong to the immunodominant antigens in Yersinia-triggered reactive arthritis: implications for autoimmunity.

BACKGROUND: Reactive arthritis (ReA) is a T cell mediated inflammatory process. The immune response is primarily directed against a triggering organism, although autoimmunity has been invoked in long-lasting, antibiotic-resistant disease. Although a variety of different species are known to trigger Reactive arthritis, the clinical manifestations are strikingly similar as well as closely associated to the HLA-B27 (70%). MATERIALS AND METHODS: Various antigenic fractions and single antigens of Yersinia enterocolitica were prepared, and their immunological activity was assessed by proliferation of synovial fluid mononuclear cells from 10 Reactive arthritis patients. The gene encoding one hitherto unknown antigen has been sequenced. Nonapeptides deduced from sequences of the target antigens were tested in an assembly assay. RESULTS: Two immunodominant proteins of Yersinia enterocolitica were found, one being the urease beta-subunit and the other the 50 S ribosomal protein L23. The latter has been sequenced and belongs to the evolutionarily conserved ribosomal proteins with homology to procaryotes and eucaryotes. One nonapeptide derived from the urease beta-subunit was identified as a possible epitope for HLA-B27-restricted cytotoxic T cells by its high affinity. This epitope is also highly conserved. CONCLUSION: Sharing of conserved immunodominant proteins between different disease triggering microorganisms could provide an explanation of the shared clinical picture in Reactive arthritis. Moreover, autoimmunity in Reactive arthritis might be mediated by antigen mimicry between evolutionarily conserved epitopes of ribosomal proteins and their host analogs.

Adolescent↗
PubMed1996

Comparison of three urease tests for detection of Helicobacter pylori in gastric biopsy specimens.

OBJECTIVE: To propose two modified urease tests for the detection of Helicobacter pylori in gastric biopsy specimens. PATIENTS AND METHODS: The presence of H. pylori infection was determined in 237 patients undergoing upper gastrointestinal endoscopy. Three media were used for the urease tests: Christensen's 2% urea broth and two urea agar media, modified by increasing the concentration of urea (to 4% and 10%) and phenol red and omitting the nutrients. RESULTS: The modified tests had good sensitivity (> 78%), specificity (96%) and accuracy (> or = 86%) at 2 h using small amounts (15%) of biopsy homogenates. They were statistically more sensitive and accurate than Christensen's broth. CONCLUSION: Both the modified 4% and 10% urea agar tests are simple, sensitive and specific and can be performed with small amounts of sample.

Bacteriological Techniques↗
PubMed1997

The enthalpimetric determination of inhibition constants for the inhibition of urease by acetohydroxamic acid.

The effect of concentration of acetohydroxamic acid (AHA) on inhibition of jack bean urease in phosphate buffer, pH 7.0, at 25 degrees C, was studied. The measurements were performed at urease concentration of 2.5 mg/100 cm3 for concentrations of urea and AHA ranging in the range of 2-50 mmol dm-3 and 0.25-10 mmol dm-3, respectively. The reactions were monitored by two techniques: analytical and enthalpimetric. For the analytical technique the growth of ammonia concentration in the course of the reaction was determined. From the recorded progress curves the following parameters were calculated for each inhibitor concentration: the initial reaction rate, the steady-state rate and the inversion constant. From these parameters the inhibition constants of the initial and steady-state stages of the reaction, Ki and Ki, were calculated. The former constant did not change whereas the latter one proved to decrease quickly with an increase in inhibitor concentration. This behaviour resulted from the fact that the inactive complex EI was not a product of internal inversion but was formed in the reaction: 2/3I + EI-->(EI.2/3I). The dissociation constant of this complex is equal to about 0.3 x 10(-3) (mol dm-3)2/3.

Enzyme Inhibitors↗
PubMed1976

Rapid-flow enthalpimetric determination of urea in serum, with use of an immobilized urease reactor.

We used a differential thermal detector in conjunction with an immobilized urease reactor to determine urea in serum. Samples (120 mul) are introduced into a flow stream and passed through an "adiabatic" column, which is packed with enough insolubilized urease to completely convert urea to ammonia and carbon dioxide. Measured temperature changes are directly proportional to the serum urea concentration. Urea in the presence of protein, bilirubin, and hemoglobin can thus be rapidly, simply, and inexpensively measured. Results correlate well with those obtained by the manual diacetyl monoxime and urease/indophenol methods.

Blood Urea Nitrogen↗
PubMed1998

Relationship between expression of HSP60, urease activity, production of vacuolating toxin, and adherence activity of Helicobacter pylori.

The relationship between the expression of heat shock protein 60 (HSP60) of Helicobacterpylori on the bacterial surface and its pathogenic factors of urease activity, production of vacuolating toxin, and adherence to human gastric carcinoma cells was examined. There was no correlation between urease activity, production of vacuolating toxin, and the expression of HSP60. However, there was a significant correlation between the adherence activity to human gastric carcinoma MKN45 cells and the expression of HSP60 (correlation coefficient; r = 0.68). In an inhibition assay with anti-HSP60 antibody, we examined the adhesion of H. pylori to MKN45 cells. The adherence of 3 of 13 H. pylori strains was inhibited by anti-HSP60 antibody. The results suggest that H. pylori HSP60 may be associated with the adhesion of H. pylori to human gastric cells.

Bacterial Adhesion↗
PubMedDate not supplied

[Effect of the temperature regimen on the kinetic and thermodynamic functions of the enzyme urease in the helminths of warm-blooded and cold-blooded animals].

The determination of the constant of the urea fission rate and study of the temperature dependence (activation energy) of the urease activity on warm- and cold-blooded animals in Ascaris suum and Contracaecum aduncum were undertaken. It has been shown that the constant of the urea fission rate in C. aduncum is more than an order of magnitude higher than that in A. suum. At a temperature of 17 degrees the rate of this process in C. aduncum changes but little while in A. suum it practically ceases. On the contrary, at 47 degrees the urease ferment activity in A. suum increases considerably while in C. aduncum the process rate does not rise as compared to that at 37 degrees. The subsequent calculations of the energy activation have shown that a certain adaptation to definite conditions of ferments functioning can take place.

Animals↗
PubMed1996

[Ni(2)(ppepO)(C(6)H(5)COO)(2)(CH(3)COOH)]ClO(4).C(4)H(10)O: Synthesis and Characterization of an Asymmetric Dinuclear Nickel(II) Complex Showing Unusual Coordination Behavior with Relevance to the Active Site of Urease.

The synthesis of the novel asymmetric ligand 1-[bis(2-pyridylmethyl)amino]-3-[2-(2-pyridyl)ethoxy]-2-hydroxypropane (ppepOH) is reported. The ligand is suitable to form asymmetric dinuclear complexes with various transition metal ions. As an example, the synthesis and X-ray structure analysis of the dinickel(II) complex [Ni(2)(ppepO)(C(6)H(5)COO)(2)(CH(3)COOH)]ClO(4).C(4)H(10)O are described. The complex crystallizes in the monoclinic space group P2(1)/n with the following unit cell parameters: a = 13.704(10) Å, b = 14.849(10) Å, c = 22.697(14) Å, beta = 96.80(5) degrees, Z = 4. The nickel(II) ions are bridged by the alkoxy donor of the ligand and two benzoate anions. The hexadentate ligand leaves a free coordination site at one of the nickel(II) ions, which is occupied by a monodentate coordinated acetic acid molecule. The coordination of the neutral acetic acid molecule is selectively stabilized by a strong intramolecular hydrogen bond of the acidic proton to the &mgr;-alkoxo bridge of the dinuclear complex. The asymmetric complex was prepared in order to mimic the substrate uptake in the dinuclear active site of ureases. The magnetic and spectroscopic properties of the complex were determined and related to those of the urease enzymes.

Journal Article↗
PubMed1999

Synthesis, Characterization, and Reactivity of Urea Derivatives Coordinated to Cobalt(III). Possible Relevance to Urease.

The syntheses of a cobalt(III) complex, 2, containing N-(2-pyridylmethyl)urea and of six complexes, 3, containing phenyl-substituted N-2-pyridylmethyl-N'-(X)phenylureas (where X = 4-H, 4-CH(3), 4-Br, 3-Cl, 4-CF(3), and 4-NO(2)), have been accomplished by reaction of [(en)(2)Co(OSO(2)CF(3))(2)](CF(3)SO(3)) with the urea ligands in tetramethylene sulfone. The complexes have been characterized by UV-vis, FTIR, (1)H NMR, and (13)C NMR spectra along with elemental analysis. Also, X-ray crystallographic analysis of 2 confirms that the urea ligand chelates as a bidentate through the pyridyl nitrogen atom and the endo deprotonated, urea nitrogen atom to form a stable five-membered ring. Crystals of the perchlorate salt of 2 were monoclinic, space group P2(1)/c with a = 9.743(1) Å, b = 13.924(3) Å, c = 15.006(4) Å, beta = 97.07(1) degrees, and Z = 4. Reflection data (3454) with I = 3sigma(I) were refined to conventional R factors of 0.037 and 0.051. In acidic solution (0.05-1.00 M HCl at 55 degrees C), the phenyl-substituted complexes undergo hydrolysis to form the bis(ethylenediamine)(2-picolylamine-N,N')cobalt(III) ion, 4, aniline, and CO(2). The hydrolysis kinetics of the phenyl-substituted complexes were studied by UV-vis spectroscopy (I = 1.00 M HCl/LiCl). At 55 degrees C the observed rate constants fit the rate law k(obsd) = kK[H(+)]/(1 + K[H(+)]). It is proposed that the protonated urea eliminates aniline to give a coordinated isocyanate intermediate that hydrolyzes rapidly to the pyridyl methylamine complex and CO(2) via the carbamate complex. Since all of the studies of this kind to date appear to involve the NCO intermediate, it raises the prospect that urease also functions by a similar path and that urease should be tested with NCO(-) as a substrate.

Journal Article↗
PubMed1983

Nickel: A micronutrient element for hydrogen-dependent growth of Rhizobium japonicum and for expression of urease activity in soybean leaves.

Soybean plants and Rhizobium japonicum 122 DES, a hydrogen uptake-positive strain, were cultured in media purified to remove Ni. Supplemental Ni had no significant effect on the dry matter or total N content of plants. However, the addition of Ni to both nitrate-grown and symbiotically grown plants resulted in a 7- to 10-fold increase in urease activity (urea amidohydrolase, EC 3.5.1.5) in leaves and significantly increased the hydrogenase activity (EC 1.18.3.1) in isolated nodule bacteroids. When cultured under chemolithotrophic conditions, free-living R. japonicum required Ni for growth and for the expression of hydrogenase activity. Hydrogenase activity was minimal or not detectable in cells incubated either without Ni or with Ni and chloramphenicol. Ni is required for derepression of hydrogenase activity and apparently protein synthesis is necessary for the participation of Ni in hydrogenase expression. The addition of Cr, V, Sn, and Pb in place of Ni failed to stimulate the activity of hydrogenase in R. japonicum and urease in soybean leaves. The evidence indicates that Ni is an important micronutrient element in the biology of the soybean plant and R. japonicum.

Journal Article↗
PubMed1985

Cytochemical Localization of Urease in a Rumen Staphylococcus sp. by Electron Microscopy.

We describe a technique whereby intracellular urease activity can be localized by transmission electron microscopy. The ammonia produced from the enzymatic hydrolysis of urea is first precipitated with sodium tetraphenylboron and then replaced with silver to produce electron-dense silver tetraphenylboron. This direct reaction product deposition procedure was used to demonstrate the presence of membrane-bound urease of Staphylococcus sp. H3-22, a gram-positive ruminal bacterium.

Journal Article↗
PubMed1977

Characteristics of unbuffered gel-immobilized urease particles. I. Internal pH.

The overall rate of reaction of a gel-immobilized urease particle necessarily depends upon the hydrogen ion concentrations within the particle. When the particle is unbuffered, the internal hydrogen ion concentrations are a consequence of the local rates of reaction and the rate of egress of the products of hydrolysis. A simple apparatus has been devised which allows a fairly rapid determination of the hydrogen ion concentration in the center of a particle for any given size, enzyme concentration, substrate concentration, and external pH. The products of urea hydrolysis are self-buffering in the region of pH 8.83 and for an external pH less than the self-buffering pH, the pH within the particle is increased because of the reaction. When the external pH is greater than the self-buffering pH, the converse occurs. The pH at the center of the particle approaches the self-buffering pH with an increase in particle size and enzyme concentration. The external increase in the external substrate concentration has a limited effect, simply rendering the local rates of reaction to be of zero order. The center-line pH and therefore all internal hydrogen ion concentrations depend upon the parameter L square root pe and the external pH. Differences between the external and center-line pH values of the order of units are unexceptional. The implications of the internal pH profiles on the local and overall rates of reaction are explored.

Acrylamides↗
PubMed1977

Characteristics of unbuffered gel-immobilized urease particles. II. Overall rate of reaction.

The overall rates of reaction of unbuffered gel-immobilized urease particles have been investigated with the aid of a packed-bed differential recycle reactor. Both substrate and enzyme concentrations have received attention. Cylindrical gel particles contained within impermeable tubelets were used to provide the physical strength necessary for the packed-bed arrangement and a one dimensional diffusion path to aid understanding of the complex interactions between substrate and product diffusion, and their effect on the reactions taking place. The experimental data have been interpreted with the aid of an enzyme rate equation (ERE) which relates the free solution characteristics of the enzyme to the conditions within a diffusion limited particle. The internal hydrogen ion profiles have been accommodated by a lumped parameter, the apparent pH (pHapp). Two methods have been suggested for the calculation of pHapp and the loss of activity on particle preparation, these methods are based on the use of the ERE in conjunction with experimental data.

Acrylamides↗
PubMed1998

The urease-catalyzed hydrolysis of thiourea and thioacetamide.

Jack bean urease catalyzes the hydrolysis of thiourea with a second-order rate constant (kcat/Km) of 1.6 (+/- 0.2) x 10(-3) M-1 S-1 at pH7, 25 degrees C. This value is lower than that for urea by a factor of 3 x 10(8). The corresponding substitution of S for O in acetamide reduces the kcat/Km value by only a factor of 33. This greater reactivity of the oxo compounds than of the corresponding thiono compounds, and the tighter binding of urea (Ks = 2.9 mM) than of either the guanidinium ion (Ki = 30 mM) or thiourea (Ki = 70 mM), suggests that the substrate chalcogen (S or O) is more likely to be stabilized in the transition state by coordination to the enzyme via a neutral hydrogen-bond donor (i.e., Brønsted acid catalysis) than by coordination via one of the active-site nickel ions (i.e., Lewis acid catalysis).

Fabaceae↗
PubMed1994

Appearance of high enzyme activity in immobilized urease disc by electron beam irradiation technique.

A new preparation method of immobilized urease discs for biomedical applications, which was a thin circular film (200 microns, 50mm phi), was developed. The method was achieved by electron beam irradiation of polyethyleneglycol diacrylate monomers in the addition of paper disc and bean powder as protective substance for irradiation by which a denaturation of the enzyme by irradiation was effectively prevented. The immobilized enzyme disc with a high enzyme activity (remaining activity yield), about 90%, was obtained. The enzyme activity was varied by the preparation conditions such as the thickness of paper disc, monomer concentration etc. The enzymes were trapped near the surface of the disc to be easily reacted with substrate. The trapped state of the enzymes appeared to be affected by a hydrophilicity of the polymers.

Electrons↗
PubMed1996

Nested-polymerase chain reaction for the detection of Helicobacter pylori infection with novel primers designed by sequence analysis of urease A gene in clinically isolated bacterial strains.

We have established a highly sensitive semi-nested PCR assay for the detection of H. pylori infection using gastric juice samples, which can be aspirated with disposable nasogastric tubes. The primers targeting H. pylori urease A gene were designed based on the sequence conservation analysis of sixteen H. pylori strains isolated from Japanese patients. The efficacy of the PCR assay, designated as the URA-PCR, was confirmed by in vitro and in vivo assessments. Its sensitivity was 97.5% in the gastric juice samples aspirated from forty patients with proven H. pylori infection, and was significantly higher than that obtained with previously described PCR assays.

Base Sequence↗
PubMed1995

Blood urea clearance with microencapsulated urease.

The response of a kidney patient to treatment using a microencapsulated urease artificial kidney (MUAK) system was modelled. The model was used to simulate the patient's response and reactor performance for an initial blood urea concentration of 10 mM and a MUAK void volume of 0.5. The performance of the reactor was strongly dependent on the enzyme activity. An optimal activity of 10 mM sec-1 was achieved in the analysis. After operation for 4 h at a flow rate of 200 ml min-1, the reduction in blood urea concentration for reactor dimensions of 2 x 10 cm, 2 x 20 cm, 4 x 10 cm and 4 x 20 cm were 38%, 52%, 60% and 62%, respectively. The effect of flow rate on the performance of urea removal was studied using the reactor dimensions of 4 x 10 cm (optimal design). The results for flow rates of 100, 200, 300 and 400 ml min-1 predicted blood urea reductions of 38, 60, 70 and 76%, respectively. Although, the conversion of urea in the reactor decreased from 100% to 96% for the respective flows of 100 to 400 ml min-1, the high turnover of reactor volume at a higher flow rate was responsible for the improved reduction of the patient's blood urea level. The model has the ability to predict the performance of the MUAK and the patient's blood urea level simultaneously, at various operating conditions.

Humans↗
PubMed1993

Comparison of urease gene primer sequences for PCR-based amplification assays in identifying the gastric pathogen Helicobacter pylori.

Different genomic DNA samples and primer sequences were evaluated in urease (ure) gene-based PCR assays for rapid identification of Helicobacter pylori. Purified DNA and heated (boiled) cell lysates of bacterial cultures from gastric biopsies were tested with three primer sets for unique internal ureA, ureA+B and ureC sequences. The heated-lysates of H. pylori were quick to prepare but more frequently gave unexpected variable or negative PCR results than assays performed on purified DNA, which were highly specific and reproducible for all three primer sets. Results indicated that sensitivity of the assay was linked to the size of the amplified target region rather than any particular strain feature, with the small 294 bp ureC product providing more accurate assays with heated-lysates of H. pylori. We strongly recommend that negative results in any PCR assay should be checked on purified DNA to exclude the possibility of a false-negative result.

Bacterial Proteins↗
PubMed1989

The influence of zinc and citrate on urease-induced urine crystallisation.

Zinc reduced and citrate promoted the urease-induced pH increase in synthetic urine. Secondary to this, the precipitation of magnesium ammonium phosphate and calcium phosphate was influenced. Independent of this pH-related effect, zinc also increased the precipitation of magnesium ammonium phosphate and decreased the calcium phosphate precipitation. These observations were not totally reproducable in human urine.

Adult↗