Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:6.3.4.6 (urease)
 7,490 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
 ...
PMID:Characteristics of a gram-negative anaerobe isolated from men with non-gonococcal urethritis. 670 82

Jack bean urease [EC 3.5.1.5] was modified with diazonium-1H-tetrazole (DHT). Reaction of DHT with the enzyme produced a characteristic absorption peak at 320 nm and led to complete loss of the enzymatic activity at a low concentration of DHT. Amino acid analysis of DHT-modified urease showed that only cysteine residues reacted with the reagent and other amino acid residues such as tyrosine, histidine, and lysine did not. The enzymatic activity was protected against DHT-inactivation by the addition of substrate. On the other hand, when the cysteine residues were modified with DHT, the enzyme was not converted to polymeric forms. Furthermore, the binding ability of urease with hydroxamic acid, a specific urease inhibitor, was virtually unaffected by DHT-inactivation. These results indicate that cysteine residues are specifically modified by DHT with concomitant loss of enzymatic activity and polymerization ability, but are not essential for the binding of hydroxamic acid to the enzyme.
 ...
PMID:Modification of thiol groups of Jack bean urease with diazonium-1H-tetrazole. 671 13

A semisolid urea-motility-indole medium designed for detection in Enterobacteriaceae of urease activity, motility, and indole production in one tube was prepared and evaluated. The formulation of the medium was similar to that of Christensen urea agar, but the agar concentration was 0.2%, and 1% tryptone was added. Results with 687 strains of Enterobacteriaceae were the same as those obtained with standard test media (98% overall agreement). The urea-motility-indole medium was also used in combination with Kligler iron agar for the recognition and differentiation of Salmonella and Shigella species from colonies picked from plating media in fecal cultures. This combination was compared with the combination of Kligler iron agar and lysine iron agar with 507 strains of non-lactose-fermenting Enterobacteriaceae. Although both combinations enabled the presumptive recognition and differentiation of Salmonella and Shigella species, an analysis of data indicated that the combination of Kligler iron agar and urea-motility-indole medium performed better than the combination of Kligler iron agar and lysine iron agar in detecting Salmonella and Shigella species.
 ...
PMID:Evaluation of Urea-motility-indole medium for recognition and differentiation of Salmonella and Shigella species in stool cultures. 721 32

The objectives were to determine the responses of turkeys to soybean meals (SBM) differing in urease and trypsin inhibitor activity, to estimate the AME of diets containing these SBM, and to determine the responses to supplemental L-Met and L-Lys. Four experiments were conducted with poults 1 to 3 wk of age and one with turkeys 6 to 8 wk of age. In Experiment 1, the trypsin inhibitor activities (TI) were 1.8, 4.2, 5.4, 7.0, and 8.8 mg trypsin inhibited/g SBM (method of Hamerstrand et al., 1981). The corresponding urease indices were .02, .14, .51, .90, and 1.5 pH units. The SBM were 46% of the diet. Significant pancreatic hypertrophy occurred with dietary concentrations of TI of 3.2 mg/g and above. At 4.0 mg TI/g of diet, the feed:gain ratio was increased, but body weight gain and AME of the diet were reduced. In Experiments 2, 3, and 4, poults responded similarly to Met additions to diets containing 46% SBM with TI of 1.8 or 4 mg/g SBM, or to Met or Met plus Lys additions to diets containing 40.7 or 49.6% SBM with TI of 2 or 11 mg/g SBM. In Experiment 5, the SBM contained TI at 4.3, 6.1, 8.9, or 12.5 mg/g. The corresponding urease indices were .05, .27, 1.43, and 1.72 pH units. The SBM were 49.6% of the diet. Using 6 to 8 wk old turkeys, the AME of the four diets were determined to be 2.76, 2.71, 2.58, and 2.57 Mcal/kg. The AME of diets containing 4.4 and 6.2 mg TI/g of diet were reduced (P < .05). In conclusion, through 3 wk of age, turkeys can tolerate soybean TI concentrations of 2.5 mg TI/g of diet. Turkeys 6 to 8 wk of age can tolerate 3 mg of soybean TI/g of diet.
 ...
PMID:Tolerance of turkeys to diets high in trypsin inhibitor activity from undertoasted soybean meals. 747 89

Wild-type Escherichia coli glutaminyl-tRNA synthetase (GlnRS; EC 6.1.1.18) poorly aminoacylates opal suppressors (GLN) derived from tRNA(Gln). Mutations in glnS (the gene encoding GlnRS) that compensate for impaired aminoacylation were isolated by genetic selection. Two glnS mutants were obtained by using opal suppressors differing in the nucleotides composing the base pair at 3.70: glnS113 with an Asp-235-->Asn change selected with GLNA3U70 (GLN carrying G3-->A and C70-->U changes), and glnS114 with a Gln-318-->Arg change selected with GLNU70 (GLN carrying a C70-->U change). The Asp-235-->Asn change was identified previously by genetic selection. Additional mutants were isolated by site-directed mutagenesis followed by genetic selection; the mutant enzymes have single amino acid changes (Lys-317-->Arg and Gln-318-->Lys). A number of mutants with no phenotype also were obtained randomly. In vitro aminoacylation of a tRNA(Gln) transcript by GlnRS enzymes with Lys-317-->Arg, Gln-318-->Lys, or Gln-318-->Arg changes shows that the enzyme's kinetic parameters are not greatly affected by the mutations. However, aminoacylation of a tRNA(Gln) transcript with an opal (UCA) anticodon shows that the specificity constants (kcat/Km) for the mutant enzymes were 5-10 times above that of the wild-type GlnRS. Interactions between Lys-317 and Gln-318 with the inside of the L-shaped tRNA and with the side chain of Gln-234 provide a connection between the acceptor end-binding and anticodon-binding domains of GlnRS. The GlnRS mutants isolated suggest that perturbation of the interactions with the inside of the tRNA L shape results in relaxed anticodon recognition.
 ...
PMID:Functional communication in the recognition of tRNA by Escherichia coli glutaminyl-tRNA synthetase. 750 18

The existence of Helicobacter pylori in the biliary tract was investigated. Seven bile samples were included in this study. Among them, six bile samples were collected by percutaneous transhepatic cholangiodrainage and the other by needle aspiration during cholecystectomy. Using nested PCR with two sets of primers homologous to the urease A gene, Helicobacter pylori DNA was detected. Three samples, one from a patient with advanced gastric cancer involving the pancreatic head and two from patients with pancreatic head tumor, were found to be positive for Helicobacter pylori DNA. On the other hand, three samples from patients with cholangiocarcinoma and one from a patient with chronic cholecystitis were all negative. To further verify the specificity of our PCR analysis, partial sequences of the PCR products from the three positive samples were analyzed by direct sequencing. Several silent mutations and a missense mutation (AAA to AGA; Lys-164 to Arg-164) were identified in the urease A gene. We conclude that Helicobacter pylori DNA can be easily detected in the bile samples. The possibility of asymptomatic cholangitis caused by this organism requires further investigation.
 ...
PMID:Detection and partial sequence analysis of Helicobacter pylori DNA in the bile samples. 758 92

The crystal structure of urease from Klebsiella aerogenes has been determined at 2.2 A resolution and refined to an R factor of 18.2 percent. The enzyme contains four structural domains: three with novel folds playing structural roles, and an (alpha beta)8 barrel domain, which contains the bi-nickel center. The two active site nickels are 3.5 A apart. One nickel ion is coordinated by three ligands (with low occupancy of a fourth ligand) and the second is coordinated by five ligands. A carbamylated lysine provides an oxygen ligand to each nickel, explaining why carbon dioxide is required for the activation of urease apoenzyme. The structure is compatible with a catalytic mechanism whereby urea ligates Ni-1 to complete its tetrahedral coordination and a hydroxide ligand of Ni-2 attacks the carbonyl carbon. A surprisingly high structural similarity between the urease catalytic domain and that of the zinc-dependent adenosine deaminase reveals a remarkable example of active site divergence.
 ...
PMID:The crystal structure of urease from Klebsiella aerogenes. 775 94

Urea production by cortical (CCD) and medullary (OMCD) collecting ducts of the rat kidney was measured in vitro by incubating single microdissected pieces of tubule in the presence of L-[guanido-14C]arginine (0.2 mM). The [14C]urea released from the cells was hydrolysed in presence of urease added to the incubation medium and the 14CO2 formed was trapped in KOH and counted. The effect of various amino acids (AA) on urea production was investigated by adding unlabelled AA (either in combination or singly) at concentrations close to those present in blood plasma. A mixture of 17 AA decreased urea production from [14C]arginine by 46% in CCD and by 58% in OMCD. When lysine and proline were omitted from the mixture, the inhibition was less marked (19% in CCD and 43% in OMCD, respectively). When AA were tested singly, lysine induced the larger inhibition (40% in CCD and 45% in OMCD), than ornithine and glutamine (about 15% each, in CCD and OMCD), whereas proline inhibition (7% in CCD, 10% in OMCD) was not statistically significant. Branched-chain amino acids (BCAA) in combination (leucine, isoleucine and valine) also markedly reduced urea production by CCD and OMCD. Their effect was dose dependent. Solubilization of CCD and OMCD cell membranes with Triton X-100 resulted in a twofold increase in urea production by control samples; the relative inhibition (per cent) induced by BCAA was enhanced, whereas that induced by lysine was decreased. The data suggest that, in living tubules, the inhibition obtained with lysine resulted, for a large part, from competition between lysine and arginine for cell uptake via a common membrane carrier, whereas the inhibition induced by BCAA corresponded to an effect on arginase activity itself.
 ...
PMID:Urea production by kidney collecting ducts in vitro: effect of amino acid addition. 805 17

Synthesis of urease by Klebsiella species is known to be induced when the nitrogen source of the growth medium is limiting, suggesting that urease gene expression is controlled by the nitrogen regulatory (ntr) system. This study showed that K. pneumoniae with mutations in either ntrA or ntrC, two integral components of the ntr system, were phenotypically urease-negative. These mutants could be complemented back to a urease positive phenotype with recombinant plasmids encoding the corresponding ntr gene. A series of ure-lacZYA transcriptional fusions, in conjunction with primer extension analysis, identified a DNA region that encoded a nitrogen-regulated promoter. This promoter region controlled transcription of ureD, the first gene in the Klebsiella pneumoniae urease gene cluster, and ureA, a gene that resides immediately downstream of ureD. A high level of transcription from the ureD promoter required NAC, a recently characterized member of the nitrogen regulatory cascade. NAC is a Lys R-like transcriptional regulator that can act at sigma 70 promoters; expression from nac itself is dependent upon NTRA. Therefore, expression of K. pneumoniae urease was dependent upon the nitrogen regulatory cascade, and transcription of at least two urease genes was from a promoter that was positively regulated by NAC.
 ...
PMID:Identification of a nitrogen-regulated promoter controlling expression of Klebsiella pneumoniae urease genes. 849 92

A mutant form of Klebsiella aerogenes urease possessing Ala instead of His at position 134 (H134A) is inactive and binds approximately half the normal complement of nickel (Park, I.-S., and Hausinger, R. P.(1993) Protein Sci. 2, 1034-1041). The crystal structure of the H134A protein was obtained at 2.0-A resolution, and it confirms that only Ni-1 of the two nickel ions found in the native enzyme is present. In contrast to the pseudotetrahedral geometry observed for Ni-1 in native urease (where it is liganded by His-246, His-272, one oxygen atom of carbamylated Lys-217, and a water molecule at partial occupancy), the mononickel metallocenter in the H134A protein was found to possess octahedral geometry and was coordinated by the above protein ligands plus three water molecules. The nickel site of H134A urease was probed by UV-visible, variable temperature magnetic circular dichroism, and x-ray absorption spectroscopies. The spectroscopic data are consistent with the presence of Ni(II) in octahedral geometry coordinated by two histidylimidazoles and additional oxygen and/or nitrogen donors. These data underscore the requirement of Ni-2 for formation of active urease and demonstrate the important role of Ni-2 in establishing the proper Ni-1 coordination geometry.
 ...
PMID:Characterization of the mononickel metallocenter in H134A mutant urease. 870 15


<< Previous 1 2 3 4 5 6 7 8 Next >>