Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

Urease possesses a dinuclear nickel active site with the metals bridged by a carbamylated lysine residue. In vitro activation of apoprotein (Apo) is achieved by incubation with Ni(II) and bicarbonate as a source of CO2. Analogues of CO2 and bicarbonate were examined for their effects on the Apo activation process. While SO2 had little effect, CS2 was shown to inhibit Apo activation via its ability to substitute for CO2 to yield an inactive dithiocarbamate-containing protein. Sulfur-to-Ni charge-transfer transitions arising from this species yielded an electronic absorption band at 324 nm with a shoulder at 382 nm. Borate, sulfate, phosphate, and molybdate had essentially no effect on Apo activation and did not substitute for bicarbonate, while treatment of Apo with Ni(II) plus vanadate led to the production of active urease containing two Ni and one V per active site. Vanadate-dependent activation of Apo resembled the normal activation process in terms of concentration of anion required, optimal pH, and incubation time needed. Furthermore, the UV-visible spectrum, maximal specific activity [386 +/- 26 U.(mg of protein)-1], Km (1.83 +/- 0.20 mM urea), and pH dependence for the vanadate-containing urease were essentially identical to properties observed for bicarbonate-activated enzyme. Vanadate-activated Apo is proposed to possess a vanadylated lysine that bridges the two Ni ions comprising its metallocenter.
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PMID:Substitution of the urease active site carbamate by dithiocarbamate and vanadate. 939 39

Urea diffusing from saliva into dental plaque is converted to ammonia and carbon dioxide by bacterial ureases. The influence of normal salivary urea levels on the pH of fasted plaque and on the depth and duration of a Stephan curve is uncertain. A numerical model which simulates a cariogenic challenge (a 10% sucrose rinse alone or one followed by use of chewing-gum with or without sugar) was modified to include salivary urea levels from 0 to 30 mmol/l. It incorporated: site-dependent exchange between bulk saliva and plaque surfaces via a salivary film; sugar and urea diffusion into plaque; pH-dependent rates of acid formation and urea breakdown; diffusion and dissociation of end-products and other buffers (acetate, lactate, phosphate, ammonia and carbonate); diffusion of protons and other ions; equilibration with fixed and mobile buffers; and charge-coupling between ionic flows. The Km (2.12 mmol/l) and Vmax (0.11 micromol urea/min/mg dry weight) values for urease activity and the pH dependence of Vmax were taken from the literature. From the results, it is predicted that urea concentrations normally present in saliva (3-5 mmol/l) will increase the pH at the base of a 0.5-mm-thick fasted plaque by up to 1 pH unit, and raise the pH minimum after a sucrose rinse or sugar-containing chewing-gum by at least half a pH unit. The results suggest that plaque cariogenicity may be inversely related to salivary urea concentrations, not only when the latter are elevated because of disease, but even when they are in the normal range.
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PMID:A mathematical model of the influence of salivary urea on the pH of fasted dental plaque and on the changes occurring during a cariogenic challenge. 943 74

C-X-C Chemokines play an important role for neutrophil extravasation through microvessels. Although the level of interleukin (IL)-8 is known to increase in the Helicobacter pylori-infected gastric mucosa, another C-X-C chemokine, GROalpha, has not been evaluated in the H. pylori-associated gastric mucosal injury. The present study was designed to investigate gastric contents of GROalpha in relation to those of IL-8 in the gastric mucosa of H. pylori-infected peptic ulcer patients. Thirty-eight patients with gastric ulcer and 41 with gastritis underwent endoscopy with informed consent and 49 were found to be H. pylori positive and 30 H. pylori negative. Biopsies from the gastric corpus were performed in each patient to examine the H. pylori colonization by bacterial culture, the rapid urease test and histological specimens as well as measurement of the contents of human GROalpha and IL-8. Helicobacter pylori infection was eradicated in 21 patients by triple therapy (lansoprazole 30 mg, amoxycillin 2.0 g, clarithromycin 600 mg; 2 weeks). The samples for GROalpha and IL-8 assay were homogenized in 0.02% aprotinin containing phosphate-buffered solution and the mucosal contents of GROalpha and IL-8 in the supernatants were quantified by sandwich enzyme immunoassay methods. The levels of GROalpha and IL-8 in H. pylori-positive gastric mucosa were significantly higher than those in the H. pylori-negative mucosa. There was a significant linear correlation between the levels of GROalpha and IL-8 (r = 0.798, P < 0.01). After the eradication of H. pylori by the triple therapy, the levels of GROalpha and IL-8 were significantly decreased. The GROalpha showed an increase in the H. pylori-positive gastric mucosa in a similar fashion as IL-8 contents, suggesting a pathogenetic role for GROalpha in H. pylori-associated gastric mucosal injury.
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PMID:Enhanced levels of C-X-C chemokine, human GROalpha, in Helicobacter pylori-associated gastric disease. 964 51

Calcium phosphate is deposited in many diseases, but formation mechanisms remain speculative. Nanobacteria are the smallest cell-walled bacteria, only recently discovered in human and cow blood and commercial cell culture serum. In this study, we identified with energy-dispersive x-ray microanalysis and chemical analysis that all growth phases of nanobacteria produce biogenic apatite on their cell envelope. Fourier transform IR spectroscopy revealed the mineral as carbonate apatite. The biomineralization in cell culture media resulted in biofilms and mineral aggregates closely resembling those found in tissue calcification and kidney stones. In nanobacteria-infected fibroblasts, electron microscopy revealed intra- and extracellular acicular crystal deposits, stainable with von Kossa staining and resembling calcospherules found in pathological calcification. Previous models for stone formation have led to an hypothesis that elevated pH due to urease and/or alkaline phosphatase activity is a lithogenic factor. Our results indicate that carbonate apatite can be formed without these factors at pH 7.4, at physiological phosphate and calcium concentrations. Nanobacteria can produce apatite in media mimicking tissue fluids and glomerular filtrate and provide a unique model for in vitro studies on calcification.
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PMID:Nanobacteria: an alternative mechanism for pathogenic intra- and extracellular calcification and stone formation. 965 77

We produced defined isogenic Helicobacter pylori ureI mutants to investigate the function of UreI, the product of one of the genes of the urease cluster. The insertion of a cat cassette had a strong polar effect on the expression of the downstream urease genes, resulting in very weak urease activity. Urease activity, measured in vitro, was normal in a strain in which ureI was almost completely deleted and replaced with a nonpolar cassette. In contrast to previous reports, we thus found that the product of ureI was not necessary for the synthesis of active urease. Experiments with the mouse-adapted H. pylori SS1 strain carrying the nonpolar ureI deletion showed that UreI is essential for H. pylori survival in vivo and/or colonization of the mouse stomach. The replacement of ureI with the nonpolar cassette strongly reduced H. pylori survival in acidic conditions (1-h incubation in phosphate-buffered saline solution at pH 2.2) in the presence of 10 mM urea. UreI is predicted to be an integral membrane protein and may therefore be involved in a transport process essential for H. pylori survival in vivo.
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PMID:The Helicobacter pylori UreI protein is not involved in urease activity but is essential for bacterial survival in vivo. 971 11

Three distinct P type pumps were cloned from H. pylori 69A. Two of these pumps, ATPase 439 and ATPase 948 (CopA), were isolated by gene library screening using DNA oligonucleotide primers. Amino acid similarities found for the predicted proteins were about 50% to Cd2+/Cu2+ pumps. Gene disruption mutagenesis rendered the H. pylori knockout mutants more sensitive to Zn2+ and Cd2+ (ATPase 439) or Cu2+ (CopA). Some of the ATPase 439-deficient mutants were negative for urease activity while the majority of the mutants remained positive. Functional diversity of the pumps was also reflected by the ion affinities found for N-terminal peptides of CopA to Cu2+ and of ATPase 439 to Ni2+, Cu2+ and CO2+. The membrane domain of the two pumps were experimentally shown to consist of eight membrane spans. When ATPase 439 was expressed under control of a tac promoter in Escherichia coli, vanadate-sensitive phosphate accumulation was observed cytochemically along the membrane of the host cells. The third P type pump (ATPase 115) which also exhibited homology to transition metal ATPase was identified by sequencing a library of H. pylori membrane genes. The hydropathy plot of this pump was very similar to the former H. pylori ATPases whereas the N-terminal ion binding region was distinct. It was concluded that, in H. pylori, the presence of three transition metal ATPases with distinct ion specificity contributes to the adaptive mechanisms for gastric survival.
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PMID:Properties and function of the P type ion pumps cloned from Helicobacter pylori. 978 54

Helicobacter pylori is a spiral Gram-negative microaerophilic bacterium that causes one of the most common infections in humans; approximately 30-50% of individuals in Western Europe are infected and the figure is nearly 100% in the developing world. It is recognized as the major aetiological factor in chronic active type B gastritis, and gastric and duodenal ulceration and as a risk factor for gastric cancer. H. pylori normally inhabits the mucus-lined surface of the antrum of the human stomach where it induces a mild inflammation, but its presence is otherwise usually asymptomatic. A variety of virulence factors appear to play a role in pathogenesis. These include the vacuolating cytotoxin VacA, cytotoxin-associated proteins, urease and motility. All are under intense study in an attempt to understand how the bacterium colonizes and persists in the gastric mucosa, and how H. pylori infections lead to the disease state. Although an explosion of research on H. pylori has occurred within the past 15 years, most efforts have been directed at aspects of the bacterium and disease process which are of direct clinical relevance. Consequently, our knowledge of many aspects of the physiology and metabolism of H. pylori is relatively poor. This should change rapidly now that the complete genome sequence of a pathogenic strain has been determined. This review focuses attention on these more fundamental areas of Helicobacter biology. Analysis of the genome sequence and some detailed metabolic studies have revealed solute transport systems, an incomplete citric acid cycle and several incomplete biosynthetic pathways, which largely explain the complex nutritional requirements of H. pylori. The microaerophilic nature of the bacterium is of particular interest and may be due in part to the involvement of oxygen-sensitive enzymes in central metabolic pathways. However, the biochemical basis for the requirement for CO2 has not been completely explained and a major surprise is the apparent lack of anaplerotic carboxylation enzymes. Although genes for glycolytic enzymes are present, physiological studies indicate that the Entner-Doudoroff and pentose phosphate pathways are more active. The respiratory chain is remarkably simple, apparently with a single terminal oxidase and fumarate reductase as the only reductase for anaerobic respiration. NADPH appears to be the preferred electron donor in vivo, rather than NADH as in most other bacteria. H. pylori is not an acidophile, and must possess mechanisms to survive stomach acid. Many studies have been carried out on the role of the urease in acid tolerance but mechanisms to maintain the protonmotive force at low external pH values may also be important, although poorly understood at present. In terms of the regulation of gene expression, there are few regulatory and DNA binding proteins in H. pylori, especially the two-component 'sensor-regulator' systems, which indicates a minimal degree of environmentally responsive gene expression.
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PMID:The physiology and metabolism of the human gastric pathogen Helicobacter pylori. 988 78

The most important phosphates involved in urinary stone disease are carbonate apatite, brushite, and struvite. Overall, phosphate stones account for 12-20% of all stones, with a downward trend for struvite and an increase in carbonate apatite being observed in the last decade. The physicochemical basis for the formation of phosphate calculi is supersaturation. Once the solubility product has been exceeded, a metastable process of supersaturation begins, with slow crystalline growth. If a critical limit of supersaturation is exceeded, large-scale spontaneous precipitation of crystals occurs in a second stage. No urinary tract infection is involved in brushite stone formation. Although infection is not a prerequisite for the formation of carbonate apatite stones, infective conditions favor carbonate apatite formation. Struvite is the characteristic infection calculus, formed as a result of urinary tract infection with urease-producing bacteria. During the first episode of urinary stone disease a definitive diagnosis of the type of stone involved is very difficult without analysis of the latter by infrared spectroscopy or X-ray diffraction. In recurrent disease, appropriate treatment can be initiated on the basis of the previous stone analysis in the majority of cases. The best means of preventing recurrent disease involving any type of phosphate stone is definitive calculus removal by shock-wave lithotripsy, percutaneous stone removal, or open surgery (especially in children). Chemolysis via acidification of the urine with Suby G solution or hemicidrin supported by oral acidification, achieved by the metabolism of L-methionine, and antibiotic therapy (especially for infectious stones) are important adjuvant modalities of therapy. After therapy of phosphate stones, metaphylaxis involving controlled urinary acidification with L-methionine supports the treatment of infection and, at a pH value of less than 6.2 and urine dilution to 2.5 l/24 h, prevents the crystallization of struvite, brushite, and carbonate apatite.
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PMID:Causes of phosphate stone formation and the importance of metaphylaxis by urinary acidification: a review. 1055 50

A phase variation in Helicobacter pylori has been previously described. In one phase the bacterium had a cell wall lipid content typical for gram-negative bacteria (HpL), whereas in the other phase the bacterium was found to have a cell wall with increased amounts of lysophospholipids (HpS). The conversion is spontaneous, but could also be induced by acid (HpS(ind)) and was associated with in vitro release of Vac A and urease. The purpose of the present study was to determine the full phospholipid content of the cell wall to indicate a molecular mechanism of the colony variation. There were no appreciable differences between the lipid profiles of HpS and HpS(ind), while there were major differences between HpL and the S-variant. In the S-variant, lysophospholipids constituted about 50% of the total phospholipids, as compared to less than 2% in the L-variant. The proportion of total and individual cholesteryl glucosides also showed considerable changes. HpL was dominated by the phosphate-linked cholesteryl glucoside (72%) while the acylated cholesteryl glucoside was the main cholesteryl glucoside of the S-variant (65%). Our results demonstrate a dramatic change in cell wall properties after acid induction and spontaneously in vitro, and suggest some molecular mechanisms for this variation from an in vitro non-virulent to a virulent variant.
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PMID:Lipid profiles of Helicobacter pylori colony variants. 1093 72

Children with fructose-1,6-diphosphatase (FDPase) deficiency often experience life threatening episodes such as ketotic hypoglycemia. We report here a rapid, simplified and sensitive method to analyze glycerol-3-phosphate (G3P) and glycerol in urine, that can be used to detect FDPase deficiency. We used the urease/direct preparation and gas chromatography-mass spectrometry in the selected-ion monitoring mode, enabling detection of G3P and glycerol level in normal controls. Using this approach, FDPase deficiency can be more easily diagnosed and differentiated from glycerol kinase deficiency or glycerol infusion patients. To date, diagnosis has been essentially based on the assay of enzymes in the liver. The proposed non-invasive method provides a clinically significant diagnostic tool that may help prevent episodic attacks.
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PMID:Rapid, simplified and sensitive method for screening fructose-1,6-diphosphatase deficiency by analyzing urinary metabolites in urease/direct preparations and gas chromatography-mass spectrometry in the selected-ion monitoring mode. 1104 42


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