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)

More than 100 strains of Corynebacterium genitalium, probably responsible for coryneform urethritis and other infections, and 600 commensals of the male and female urogenital tracts have been studied and grouped into five pathogenic types numbered I to V and six saprophytic types designated C-1 to C-6 on the basis of eight biological reactions. This preliminary classification has been based on differences in requirements for oxygen, on the fermentation of fructose, dextrose, sucrose, and starch together with the production of the enzymes gelatinase, lipase, and urease. One criterion differentiated the pathogens from the commensals: All pathogens were nonfructose fermenters whereas every commensal fermented this sugar.
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PMID:A diagnostic key employing biological reactions for differentiating pathogenic Corynebacterium genitalium (NSU corynebacteria) from commensals of the urogenital tract. 35 42

Hydrolysis of arginine into urea and ornithine (Orn) was observed to take place in several segments of the rat nephron including cortical and medullary pars recta of the proximal tubule (PST) and collecting duct (CD). This work was now extended to the adult mouse and rabbit. Representative nephron segments, obtained by microdissection of collagenase-treated kidneys, were incubated with L-[guanido-14C]arginine (216 microM). Addition of urease produced 14CO2 + 2 NH3 from the newly formed urea released in the incubate. 14CO2 was trapped in KOH and counted. In both species, as well as in the rat, the PST was the site of the highest urea + Orn production, with an intensity increasing from cortex to medulla. For other nephron segments, the pattern was not similar in all species. Significant production of urea + Orn was observed in the proximal convoluted tubule and the medullary thick ascending limb in the rabbit, but not in the CD of either the rabbit or the mouse. The functional significance of this urea + Orn production remains unclear. The total amount of urea generated intrarenally by this reaction does not seem sufficient to play a significant role in the urinary concentrating mechanism. It may be assumed that Orn could be further metabolized to polyamines and play a role in maintaining cell integrity and function in the PST, especially in its medullary part, exposed to hypertonicity and poor oxygen supply.
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PMID:Localization of urea and ornithine production along mouse and rabbit nephrons: functional significance. 144 76

Microbioassays using bacteria or enzymes are increasingly applied to measure chemical toxicity in the environment. Attractive features of these assays may include low cost, rapid response to toxicants, high sample throughput, modest laboratory equipment and space requirements, low sample volume, portability, and reproducible responses. Enzymatic tests rely on measurement of either enzyme activity or enzyme biosynthesis. Dehydrogenases are the enzymes most used in toxicity testing. Assay of dehydrogenase activity is conveniently carried out using oxidoreduction dyes such as tetrazolium salts. Other enzyme activity tests utilize ATPases, esterases, phosphatases, urease, luciferase, beta-galactosidase, protease, amylase, or beta-glucosidase. Recently, the inhibition of enzyme (beta-galactosidase, tryptophanase, alpha-glucosidase) biosynthesis has been explored as a basis for toxicity testing. Enzyme biosynthesis was found to be generally more sensitive to organic chemicals than enzyme activity. Bacterial toxicity tests are based on bioluminescence, motility, growth, viability, ATP, oxygen uptake, nitrification, or heat production. An important aspect of bacterial tests is the permeability of cells to environmental toxicants, particularly organic chemicals of hydrophobic nature. Physical, chemical, and genetic alterations of the outer membrane of E. coli have been found to affect test sensitivity to organic toxicants. Several microbioassays are now commercially available. The names of the assays and their basis are: Microtox (bioluminescence), Polytox (respiration), ECHA Biocide Monitor (dehydrogenase activity), Toxi-Chromotest (enzyme biosynthesis), and MetPAD (enzyme activity). An important feature common to these tests is the provision of standardized cultures of bacteria in freeze-dried form. Two of the more recent applications of microbioassays are in sediment toxicity testing and toxicity reduction evaluation. Sediment pore water may be assayed directly or solvents may be used to extract the toxicants. Some of the solvents used for extraction of organic chemicals are themselves toxic to bacteria (e.g., dichloromethane), requiring exchange with a less toxic solvent (e.g., ethanol, methanol, DMSO). A modification of the Microtox test allows direct assay of solid-phase samples such as sediments. The toxicity reduction evaluation (TRE) must be carried out at wastewater treatment plants whose effluents fail toxicity standards. The TREs require numerous and repeated toxicity assays, thus favoring application of microbioassays. Presently, no single microbioassay can detect all categories of environmental toxicants with equal sensitivity. Therefore, a battery of tests approach is recommended. The differential sensitivity of alternative tests may, in fact, be exploited. Further research is needed to construct strains of genetically engineered microorganisms or isolate microorganisms or enzymes that respond to specific classes of toxicants. These can be combined into batteries appropriate for different environments or test objectives.
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PMID:Bacterial and enzymatic bioassays for toxicity testing in the environment. 150 75

The mechanism for Helicobacter pylori-induced gastric mucosal injury remains obscure. H. pylori has high urease activity to produce ammonia from urea in the stomach. In this study, the effects of ammonia on (a) gastric mucosal integrity, (b) gastric mucosal hemodynamics, (c) mucosal cellular viability, (d) mitochondrial respiration, and (e) energy metabolism of gastric mucosal were investigated. Ammonia (pH 10.3) at concentrations of greater than 125 mmol/L caused acute macroscopic gastric mucosal lesions in a dose-dependent manner, whereas glycine-NaOH buffer (pH 10.3) or ammonium chloride (pH 4.5) did not. The decrease in energy charge preceded the occurrence of gastric mucosal lesions, but ammonia caused no change in mucosal hemodynamics. Oxygen consumption of isolated cells and mitochondria of gastric mucosa was inhibited by ammonia dose-dependently. The present results indicate that ammonia impairs mitochondrial and cellular respiration and energy metabolism and that ammonia decreases mucosal cell viability, leading subsequently to mucosal damage.
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PMID:Mechanism of gastric mucosal damage induced by ammonia. 158 7

The inflammatory lesions associated with Helicobacter pylori gastritis and duodenitis contain large numbers of mononuclear cells. The close proximity of H. pylori to gastric mucosa suggests that the organism interacts with mononuclear cells, thereby modulating the inflammatory response. To investigate the role of monocytes/macrophages in this response, we examined the effect of whole H. pylori bacteria, H. pylori surface proteins, and H. pylori lipopolysaccharide (LPS) on purified human monocytes. Whole H. pylori and the extracted LPS induced expression of the monocyte surface antigen HLA-DR and interleukin-2 receptors, production of the inflammatory cytokines interleukin 1 and tumor necrosis factor (peptide and messenger RNA), and secretion of the reactive oxygen intermediate superoxide anion. Since H. pylori in vivo does not invade mucosal tissue, we determined whether soluble constituents of the bacteria could activate monocytes. Soluble H. pylori surface proteins, which are enriched for urease and do not contain LPS, stimulated phenotypic, transcriptional, and functional changes consistent with highly activated monocytes. These findings indicate that H. pylori is capable of activating human monocytes by an LPS-independent as well as an LPS-dependent mechanism. H. pylori activation of resident lamina propria macrophages and monocytes trafficking through the mucosa, leading to the secretion of increased amounts of inflammatory cytokines and reactive oxygen intermediates, could play an important role in mediating the inflammatory response associated with H. pylori gastritis and duodenitis.
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PMID:Soluble surface proteins from Helicobacter pylori activate monocytes/macrophages by lipopolysaccharide-independent mechanism. 184 39

Urea metabolism was studied with nitrogen-starved cells of Chlorella vulgaris Beijerinck var. viridis (Chodat), a green alga which apparently lacks urease. Incorporation of radioactivity from urea-(14)C into the alcohol-soluble fraction was virtually eliminated in cell suspensions flushed with 10% CO(2) in air. This same result was obtained when expected acceptors of urea carbon were replenished by adding ornithine and glucose with the urea. Several carbamyl compounds, which might be early products of urea metabolism and a source of the (14)CO(2), were not appreciably labeled. If cells were treated with cyanide at a concentration which inhibited ammonia uptake completely and urea uptake only slightly, more than half of the urea nitrogen taken up was found in the medium as ammonia. Cells under nitrogen gas in the dark were unable to take up urea or ammonia, but the normal rate of uptake was resumed in light. Since 3-(3,4-dichlorophenyl)-1,1-dimethylurea did not selectively inhibit this uptake, an active respiration supported by light-dependent oxygen evolution in these cells was ruled out. A tentative scheme for urea metabolism is proposed to consist of an initial energy-dependent splitting of urea into carbon dioxide and ammonia. This reaction in Chlorella is thought to differ from a typical urease-catalyzed reaction by the apparent requirement of a high energy compound, possibly adenosine triphosphate.
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PMID:Metabolism of urea by Chlorella vulgaris. 578 73

We investigated the regulation of genes concerned with nitrogen metabolism by oxygen in the facultative anaerobe Klebsiella pneumoniae. We found oxygen to be required for the expression of the hut operons; the effect of O2 on the glutamine synthetase and urease was less pronounced than on the hut operons. Glutamine synthetase was transiently repressed during the transition from an aerobic to an anaerobic environment. Regulation of hut by O2 suppressed the effect of nitrogen limitation on the expression of these genes.
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PMID:Regulation of Klebsiella pneumoniae hut operons by oxygen. 610 51

A small, fastidious gram-negative anaerobe was isolated from men with non-gonococcal urethritis (NGU). The isolates are described as NGU-associated anaerobes because they were extremely rare in men with urethritis other than NGU, and in asymptomatic men. They showed twitching motility, had many polar pili and appeared to be a homogenous group culturally, morphologically and biochemically. None of the strains fermented or utilised carbohydrates or organic acids as sole sources of carbon for energy and growth. However, growth of all strains was stimulated by formate and fumarate in liquid and solid media, especially in the former where growth seemed dependent on these growth factors. Unlike most anaerobes they produced cytochrome enzyme(s) that might be involved in oxidation-reduction reactions in the presence of oxygen as some of the strains were capable of growing in 5% oxygen. However, growth and energy generally resulted from anaerobic phosphorylation. Strains of this anaerobe seemed to require a low redox-potential (Eh) for survival during transportation but this was not essential for growth. Comparative studies with the other asaccharolytic anaerobes showed some similarity between the NGU-associated anaerobe, Bacteroides ureolyticus and Wolinella succinogenes. Like these, some NGU-associated strains pitted agar media and all produced urease. However, unlike these anaerobes, strains of the NGU-associated anaerobe produced enzymes for the hydrolysis of arginine, and the decarboxylation of lysine and ornithine. They also produced oxidase and some strains haemolysed sheep red cells. However, lactic acid was not an end-product of the metabolism of glucose by any of the strains. The NGU-associated anaerobes are strikingly different from anaerobic vibrios, B. praeacutus and B. asaccharolyticus.
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PMID:Characteristics of a gram-negative anaerobe isolated from men with non-gonococcal urethritis. 670 82

A simple and inexpensive procedure for determination of microgram quantities of metal ions in proteins is described and tested with nickel and iron. The method involves (a) dry ashing in an oxygen atmosphere at 450-460 degrees C in Pyrex vessels, (b) conversion of the metal oxides or other compounds to readily soluble species, and (c) spectrophotometric analysis. An improved procedure for the direct spectrophotometric determination of nickel using dimethylglyoxime is accurate to +/- 2% or better with samples of 1-5 microgram of nickel. These techniques were used to determine that the nickel content of freshly prepared jack bean urease in 2.00 +/- 0.12 g-at./96 600 g protein. The corresponds to 2.0 nickel ions per subunit. This result was confirmed by atomic absorption analysis, which also showed that calcium, manganese, cobalt, and iron are not present in significant amounts in urease.
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PMID:Jack bean urease (EC 3.5.1.5). I. A simple dry ashing procedure for the microdetermination of trace metals in proteins. The nickel content of urease. 727 35

Helicobacter pylori infection is characterized by an inflammatory response in the gastric epithelium, the intensity of which appears to be type-strain specific. Infections caused by Type 1 H. pylori organisms, i.e., those expressing VacA (the cytotoxin) and CagA (the cytotoxin-associated protein), are associated with a strong polymorph mucosal infiltration in vivo, and with increased secretion of interleukin-8 by epithelial cells. The inflammatory potential of Type II strains (non-cytotoxic, VacA- and CagA-negative) is probably less pronounced. The small urease subunit, porins, and other substances produced by H. pylori show neutrophil chemotactic activities in vitro. These bacterial components promote the adhesion of polymorphs to endothelial cells and stimulate polymorphs to generate oxygen reactive metabolites. This can severely damage the gastroduodenal mucosa.
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PMID:Progress in defining the inflammatory cascade. 760 Jan 33


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