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)

Poly(acrylonitrile-methylmethacrylate-sodium vinylsulfonate) membranes were subjected to seven different chemical modifications and the amount of the newly formed groups was measured for each membrane. Urease was then covalently immobilized onto the modified membranes and the amount of bound protein was determined. The kinetic parameters V(max) and K(m) of the immobilized urease were studied under static and dynamic conditions. Results showed that the rate of the enzyme reaction was higher for the membranes modified with NH(2)OH . H(2)SO(4), NH(2)NH(2) . H(2)SO(4), NaOH + EDA and NaOH + GA + EDA. It was confirmed that the reaction rate, measured under dynamic conditions, was higher than that one determined under static conditions. The influence of Cu(II) ions, as inhibitors, on the enzyme reaction kinetics (V(i) and K(i)) was also investigated. It turned out that the most sensitive membranes towards Cu(II) were those modified with NH(2)NH(2) . H(2)SO(4), NaOH + EDA and H(2)O(2). The results initiated further investigations on the influence of other heavy metal ions (Cd(II), Zn(II), Ni(II) and Pb(II)) over urease bound to a NH(2)OH . H(2)SO(4)-modified membrane. It was found that the inhibition effect of the heavy metal ions over immobilized urease decreases in the order: Cu(II) > Cd(II) > Zn(II) > Ni(II) > Pb(II). [Diagram: see text]
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PMID:Kinetic parameters of urease immobilized on modified acrylonitrile copolymer membranes in the presence and absence of Cu(II) ions. 1589 77

The hyp operon encodes accessory proteins that are required for the maturation of the [NiFe] hydrogenase enzymes and, in some organisms, for the production of urease enzymes as well. HypA or a homologous protein is required for nickel insertion into the hydrogenase precursor proteins. In this study, recombinant HypA from Escherichia coli was purified and characterized in vitro. Metal analysis was used to demonstrate that HypA simultaneously binds stoichiometric Zn(2+) and stoichiometric Ni(2+). Competition experiments with a metallochromic indicator reveal that HypA binds zinc with nanomolar affinity. Spectroscopic analysis of cobalt-containing HypA provides evidence for a tetrathiolate coordination sphere, suggesting that the zinc site has a structural role. In addition, HypA can exist as several oligomeric complexes and the zinc content modulates the quaternary structure of the protein. Fluorescence titration experiments demonstrate that HypA binds nickel with micromolar affinity and that the presence of zinc does not dramatically affect the nickel-binding activity. Finally, complex formation between HypA and HypB, another accessory protein required for nickel insertion, was observed. These experiments suggest that HypA is an architectural component of the hydrogenase metallocenter assembly pathway and that it may also have a direct role in the delivery of nickel to the hydrogenase large subunit.
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PMID:Escherichia coli HypA is a zinc metalloprotein with a weak affinity for nickel. 1599 83

Actions and interactions of heavy metals (cadmium, zinc and plumbum) and polycyclic aromatic hydrocarbons (PAHs) [phenanthrene, fluoranthene, benzo(a)pyrene] on the soil urease and dehydrogenase activity were studied after 49 days exposure. The experimental approach was based on the uniform design which can cut the experiment time and improve the efficiency of experiments. Data treatment was essentially based on the multiple regression technique. The results showed that the action and interaction between heavy metals and PAHs were strongly dependent on the time of pollution. The dehydrogenase exhibits more sensitive to the combined pollution than urease. The negative interaction between Zn and Cd to hydrogenase activity and the combined stimulatory activity of Phenanthrene and Benzo(a)pyrene (or fluoranthene) to soil enzyme were observed. The interactions between Zn (Cd) and phenanthrene towards urease (dehydrogenase) were positive, and the interaction between Zn and benzo(a)pyrene to urease activity was negative. This study corresponds to exploratory phase in order to reveal interaction effects of heavy metals and PAHs on the soil enzyme and then to set up more in-depth analysis to increase progressively the understanding of the ecotoxicological mechanisms involved.
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PMID:Interaction of polycyclic aromatic hydrocarbons and heavy metals on soil enzyme. 1626 87

Actions and interactions between heavy metals (HM)-cadmium, zinc, lead, and polycyclic aromatic hydrocarbons (PAHs)-phenanthrene, fluoranthene, benzo(a)pyrene toward soil urease activity were studied after 7, 14, 21, and 28 days of exposure under controlled conditions. The experimental approach was based on the uniform design. Ten different contamination conditions were studied simultaneously, with 10 concentration levels for each pollutant. Data treatment was essentially based on the multiple regression technique. The results showed that Zn interacted more easily with PAHs than Pb or Cd. On the first 7 days of incubation, zinc alone reduced the urease activity more significantly than any other pollutants and no significant interactions between PAH and HM were observed. From 14 to 21 days of incubation, the interaction between Zn and benzo(a)pyrene decreased the soil urease activity. At 14 days, the interaction between Zn and phenanthrene was antagonistic (less than additive), while at 21 days it was synergistic (more than additive). At 28 days, the interaction between phenanthrene and fluoranthene was synergistic. This study indicated that the combined effect of PAH and HM on soil urease activity depends largely on the incubation time. Uniform design appears to be a good method for investigating the combined effect of PAH and HM.
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PMID:Combined effect of heavy metals and polycyclic aromatic hydrocarbons on urease activity in soil. 1640 98

Maintaining metal homeostasis is crucial for the adaptation of Helicobacter pylori to the gastric environment. Iron, copper, and nickel homeostasis has recently been demonstrated to be required for the establishment of H. pylori infection in animal models. Here we demonstrate that the HP0969-0971 gene cluster encoding the Czc-type metal export pump homologs HP0969, HP0970, and the H. pylori-specific protein HP0971 forms part of a novel H. pylori metal resistance determinant, which is required for gastric colonization and for the modulation of urease activity. Insertional mutagenesis of the HP0971, HP0970, or HP0969 genes in H. pylori reference strain 26695 resulted in increased sensitivity to cadmium, zinc, and nickel (czn), suggesting that the encoded proteins constitute a metal-specific export pump. Accordingly, the genes were designated cznC (HP0971), cznB (HP0970), and cznA (HP0969). The CznC and CznA proteins play a predominant role in nickel homeostasis, since only the cznC and cznA mutants but not the cznB mutant displayed an 8- to 10-fold increase in urease activity. Nickel-specific affinity chromatography demonstrated that recombinant versions of CznC and CznB can bind to nickel and that the purified CznB protein interacted with cadmium and zinc, since both metals competitively inhibited nickel binding. Finally, single cznA, cznB, and cznC mutants did not colonize the stomach in a Mongolian gerbil-based animal model. This demonstrates that the metal export functions of H. pylori cznABC are essential for gastric colonization and underlines the extraordinary importance of metal ion homeostasis for the survival of H. pylori in the gastric environment.
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PMID:The novel Helicobacter pylori CznABC metal efflux pump is required for cadmium, zinc, and nickel resistance, urease modulation, and gastric colonization. 1679 Jul 56

We sought to explore the relationship between Helicobacter pylori infection and serum ferritin, vitamin B(12), folate, and zinc status among children. Fifty patients aged 5-18 years who underwent upper gastrointestinal endoscopy because of dyspeptic symptoms, were studied, prospectively. Patients were grouped as H. pylori positive (group 1, n=32) or H. pylori negative (group 2, n=18) by histopathologic examination and rapid urease test. Fasting serum ferritin, vitamin B(12), folate, and zinc levels of patients were measured. Both groups were indifferent according to age, gender, height standard deviation score (H(SDS)), and weight standard deviation score (W(SDS)). Serum ferritin levels were 33+/-26 and 50+/-46 ng/mL (P=.098), vitamin B(12) levels were 303+/-135 and 393+/-166 pg/mL (P=.042), folate levels were 9.64+/-3.2 and 9.61+/-2.8 ng/mL (P=.979), and zinc levels were 95+/-48 and 87+/-31 mug/dL (P=.538), in groups 1 and 2, respectively. Ferritin levels of 14 (43.8%) patients in group 1 and 6 (33.3%) patients in group 2 were below the normal range (P=.470). Serum vitamin B(12) levels of 9 children (28%) in group 1 and 2 children (11%) in group 2 were below the normal range (P=.287). The findings of the present study suggest that H. pylori infection has a negative effect on serum ferritin and vitamin B(12) levels in children. This negative effect on vitamin B(12) levels is rather marked in contrast to that on ferritin levels. H. pylori infection has no significant effect on serum folate or zinc levels among children.
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PMID:Serum ferritin, vitamin B(12), folate, and zinc levels in children infected with Helicobacter pylori. 1721 8

Heavy metal (HM) is a major hazard to the soil-plant system. This study investigated the combined effects of cadium (Cd), zinc (Zn) and lead (Pb) on activities of four enzymes in soil, including calatase, urease, invertase and alkalin phosphatase. HM content in tops of canola and four enzymes activities in soil were analyzed at two months after the metal additions to the soil. Pb was not significantly inhibitory than the other heavy metals for the four enzyme activities and was shown to have a protective role on calatase activity in the combined presence of Cd, Zn and Pb; whereas Cd significantly inhibited the four enzyme activities, and Zn only inhibited urease and calatase activities. The inhibiting effect of Cd and Zn on urease and calatase activities can be intensified significantly by the additions of Zn and Cd. There was a negative synergistic inhibitory effect of Cd and Zn on the two enzymes in the presence of Cd, Zn and Pb. The urease activity was inhibited more by the HM combinations than by the metals alone and reduced approximately 20%-40% of urease activity. The intertase and alkaline phosphatase activities significantly decreased only with the increase of Cd concentration in the soil. It was shown that urease was much more sensitive to HM than the other enzymes. There was a obvious negative correlation between the ionic impulsion of HM in soil, the ionic impulsion of HM in canola plants tops and urease activity. It is concluded that the soil urease activity may be a sensitive tool for assessing additive toxic combination effect on soil biochemical parameters.
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PMID:Effects of cadium, zinc and lead on soil enzyme activities. 1729 54

The two Ni2+ ions in the urease active site are delivered by the metallochaperone UreE, whose metal binding properties are central to the assembly of this metallocenter. Isothermal titration calorimetry (ITC) has been used to quantify the stoichiometry, affinity, and thermodynamics of Ni2+, Cu2+, and Zn2+ binding to the well-studied C-terminal truncated H144*UreE from Klebsiella aerogenes, Ni2+ binding to the wild-type K. aerogenes UreE protein, and Ni2+ and Zn2+ binding to the wild-type UreE protein from Bacillus pasteurii. The stoichiometries and affinities obtained by ITC are in good agreement with previous equilibrium dialysis results, after differences in pH and buffer competition are considered, but the concentration of H144*UreE was found to have a significant effect on metal binding stoichiometry. While two metal ions bind to the H144*UreE dimer at concentrations <10 microM, three Ni2+ or Cu2+ ions bind to 25 microM dimeric protein with ITC data indicating sequential formation of Ni/Cu(H144*UreE)4 and then (Ni/Cu)2(H144*UreE)4, or Ni/Cu(H144*UreE)2, followed by the binding of four additional metal ions per tetramer, or two per dimer. The thermodynamics indicate that the latter two metal ions bind at sites corresponding to the two binding sites observed at lower protein concentrations. Ni2+ binding to UreE from K. aerogenes is an enthalpically favored process but an entropically driven process for the B. pasteurii protein, indicating chemically different Ni2+ coordination to the two proteins. A relatively small negative value of DeltaCp is associated with Ni2+ and Cu2+ binding to H144*UreE at low protein concentrations, consistent with binding to surface sites and small changes in the protein structure.
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PMID:Thermodynamics of Ni2+, Cu2+, and Zn2+ binding to the urease metallochaperone UreE. 1771 1

The biosynthesis of the active metal-bound form of the nickel-dependent enzyme urease involves the formation of a lysine-carbamate functional group concomitantly with the delivery of two Ni(2+) ions into the precast active site of the apoenzyme and with GTP hydrolysis. In the urease system, this role is performed by UreG, an accessory protein belonging to the group of homologous P-loop GTPases, often required to complete the biosynthesis of nickel-enzymes. This study is focused on UreG from Helicobacter pylori (HpUreG), a bacterium responsible for gastric ulcers and cancer, infecting large part of the human population, and for which urease is a fundamental virulence factor. The soluble HpUreG was expressed in E. coli and purified to homogeneity. On-line size exclusion chromatography and light scattering indicated that apo-HpUreG exists as a monomer in solution. Circular dichroism, which demonstrated the presence of a well-defined secondary structure, and NMR spectroscopy, which revealed a large number of residues that appear structured on the basis of their backbone amide proton chemical shift dispersion, indicated that, at variance with other UreG proteins so far characterized, this protein is significantly folded in solution. The amino acid sequence of HpUreG is 29% identical to that of HypB from Methanocaldococcus jannaschii, a dimeric zinc-binding GTPase involved in the in vivo assembly of [Ni,Fe]-hydrogenase. A homology-based molecular model of HpUreG was calculated, which allowed us to identify structural and functional features of the protein. Isothermal titration microcalorimetry demonstrated that HpUreG specifically binds 0.5 equivalents of Zn(2+) per monomer (K(d) = 0.33 +/- 0.03 microM), whereas it has 20-fold lower affinity for Ni(2+) (K(d) = 10 +/- 1 microM). Zinc ion binding (but not Ni(2+) binding) causes protein dimerization, as confirmed using light scattering measurements. The structural rearrangement occurring upon Zn(2+)-binding and consequent dimerization was evaluated using circular dichroism and fluorescence spectroscopy. Fully conserved histidine and cysteine residues were identified and their role in zinc binding was verified by site-directed mutagenesis and microcalorimetry. The results are analyzed and discussed with respect to analogous examples of GTPases in nickel metabolism.
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PMID:Zn2+-linked dimerization of UreG from Helicobacter pylori, a chaperone involved in nickel trafficking and urease activation. 1876 50

NikR is a prokaryotic transcription factor that regulates the expression of Ni2+ enzymes and other proteins involved in Ni2+ trafficking. In the human pathogen Helicobacter pylori, NikR controls transcription of the Ni2+ enzyme urease, which allows survival of the bacterium in the acidic gastric niche. The in vitro affinity of NikR from H. pylori (HpNikR) for different metal ions and the metal-ion-dependent capability of HpNikR to bind PureA, the promoter of the urease operon, were the object of this study. Electrophoretic mobility shift and DNase I footprinting assays indicated that Ni2+ is necessary and sufficient to promote HpNikR binding to PureA, while the effect of other metal ions in identical conditions is significantly lower (Zn2+ and Co2+) or absent (Ca2+ and Mg2+). Isothermal titration calorimetry (ITC) demonstrated the absence of specific Ca2+ and Mg2+ binding to the protein. ITC also established the binding of Zn2+ and Co2+ to two sets of high-affinity sites on HpNikR, differing in stoichiometry (n1=2, n2=4) and dissociation constant (Kd1=6 nM, Kd2=90 nM for Zn2+; Kd1=0.3 microM, Kd2=2.7 microM for Co2+). Additional low-affinity binding sites were observed for Zn2+ (n=8, Kd=1.6 microM). Mobility shift assays and ITC proved that binding of stoichiometric Ni2+ (but not Zn2+ or Co2+) to the high-affinity sites (but not to the low-affinity sites) selectively activates HpNikR to bind its target operator with 1:1 stoichiometry and Kd=56 nM. A protein conformational rearrangement is selectively induced by Ni2+ and not by Zn2+, as indicated by fluorescence spectroscopy and microcalorimetry. Accordingly, competition experiments showed that stoichiometric Ni2+ outperforms Zn2+, as well as Co2+, in functionally activating HpNikR toward high affinity binding to PureA. A general scheme for the nickel-selective HpNikR-DNA interaction is proposed.
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PMID:High-affinity Ni2+ binding selectively promotes binding of Helicobacter pylori NikR to its target urease promoter. 1879 Jun 98


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