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:1.12.7.2 (hydrogenase)
3,522 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Alcaligenes eutrophus strain CH34, which was isolated as a bacterium resistant to cobalt, zinc, and cadmium ions, shares with A. eutrophus strain H16 the ability to grow lithoautotrophically on molecular hydrogen, to form a cytoplasmic NAD-reducing and a membrane-bound hydrogenase, and most metabolic attributes; however, it does not grow on fructose. Strain CH34 contains two plasmids, pMOL28 (163 kilobases) specifying nickel, mercury, and cobalt resistance and pMOL30 (238 kilobases) specifying zinc, cadmium, mercury, and cobalt resistance. The plasmids are self-transmissible in homologous matings, but at low frequencies. The transfer frequency was strongly increased with IncP1 plasmids RP4 and pUZ8 as helper plasmids. The phenotypes of the wild type, cured strains, and transconjugants are characterized by the following MICs (Micromolar) in strains with the indicated phenotypes: Nic+, 2.5; Nic-, 0.6; Cob+A, 5.0; Cob+B, 20.0; Cob-, less than 0.07; Zin+, 12.0; Zin-, 0.6; Cad+, 2.5; and Cad-, 0.6. Plasmid-free cells of strain CH34 are still able to grow lithoautotrophically and to form both hydrogenases, indicating that the hydrogenase genes are located on the chromosome, in contrast to the Hox structural genes of strain H16, which are located on the megaplasmid pHG1 (450 kilobases).
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PMID:Alcaligenes eutrophus CH34 is a facultative chemolithotroph with plasmid-bound resistance to heavy metals. 388 93

Incubation of native, reduced Clostridium pasteurianum ferredoxin with different metals gave a range of modifications in the electronic and EPR spectrum of the protein, or made the signals disappear. The reduced protein, isolated after incubation with different metals under identical conditions (50 microM protein, 1 mM metal, 1 h incubation) was found to contain amounts of foreign metals increasing with their thiophylicity, i.e. Cd2+ >> Zn2+ > Co2+. Little, if any, incorporation was observed for Ni2+, Cu2+, Mn2+ or in the absence of reductant. The activity of substituted ferredoxins in a hydrogenase-coupled assay was proportional to the amount of residual iron, suggesting that the residual iron is present in a population of intact active molecules rather than in partially substituted clusters distributed among individual molecules. The cadmium-substituted ferredoxin did not contain iron, but contained eight cadmium atoms and six labile sulfide atoms/mol. Folding of the isolated, substituted proteins was investigated by CD and 1H-NMR. Both techniques showed retention of the main structural features of the protein upon metal substitution. The rate and extent of the substitution of iron by cadmium were essentially independent of pH, but were found to decrease with increasing ionic strength and to increase with the cadmium concentration. In the cadmium-substituted protein, cadmium was replaced by iron upon incubation with iron and mercaptoethanol in the absence of dithionite. In the presence of dithionite, cadmium was not replaced by iron upon incubation of the cadmium-substituted protein with excess iron and mercaptoethanol. In competition experiments, incubation of iron-containing ferredoxin with stoichiometric amounts of cadmium in the presence of dithionite and excess iron and mercaptoethanol resulted in quantifiable replacement of iron by cadmium. Therefore, substitution of iron by cadmium was only achieved under reducing conditions, and was only reversible in the absence of strong reductants.
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PMID:Reversible and non-denaturing replacement of iron by cadmium in Clostridium pasteurianum ferredoxin. 802 May 1

The maturation of [NiFe] hydrogenases includes formation of the nickel metallocenter, proteolytic processing of the metal center carrying large subunit, and its assembling with other hydrogenase subunits. The hydrogenase maturating enzyme HYBD from Escherichia coli, a protease of molecular mass 17.5 kDa, specifically cleaves off a 15 amino acid peptide from the C terminus of the precursor of the large subunit of hydrogenase 2 in a nickel-dependent manner. Here we report the crystal structure of HYBD at 2.2 A resolution. It consists of a twisted five-stranded beta-sheet surrounded by four and three helices, respectively, on each side. A cadmium ion from the crystallization buffer binds to the proposed nickel-binding site and is penta-coordinated by Glu16, Asp62, His93, and a water molecule in a pseudo-tetragonal arrangement. HYBD is topologically related to members of the metzincins superfamily of zinc endoproteinases, sharing the central beta-sheet and three helices. In contrast to the metzincins, the metal-binding site of HYBD is localized at the C-terminal end of the beta-sheet. Three helical insertions unique to HYBD pack against one side of the sheet, build up the active site cleft, and provide His93 as ligand to the metal. From this structure, we derive molecular clues into how the protease HYBD is involved in the hydrogenase maturation process.
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PMID:Crystal structure of the hydrogenase maturating endopeptidase HYBD from Escherichia coli. 1033 25

The interaction of the hydrogenase maturation endopeptidase HycI with its substrate, the precursor of the large subunit, was studied. Replacement of conserved amino-acid residues in HycI, which have been shown to bind a cadmium ion from the crystallization buffer in crystals of HybD (endopeptidase for hydrogenase 2), abolished or strongly reduced processing activity. Atomic absorption spectroscopy of purified HycI and HybD proteins showed the absence of nickel. In vitro processing assays showed that the reaction requires nickel to be bound to the precursor and the protease does not have a function in nickel delivery to the substrate. Radioactive labelling of cells with 63Ni, devoid of endopeptidase, resolved several forms of the precursor which are possibly intermediates in the maturation pathway. It is concluded that the endopeptidase uses the metal in the large subunit of [NiFe]-hydrogenases as a recognition motif.
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PMID:Nickel serves as a substrate recognition motif for the endopeptidase involved in hydrogenase maturation. 1072 38

The effects of some metal ions on the activity and activation of Thiocapsa roseopersicina hydrogenase have been studied. Inhibitory effects of Ni2+ and Cd2+ on the catalytic activity of the enzyme were reversible and competitive with respect to methyl viologen (MV) in the reaction of hydrogen oxidation. The affinity of these metal ions to the enzyme increased significantly with increasing pH, suggesting that their interactions are determined by electrostatic forces. Cu2+ and Hg2+ irreversibly inhibited the hydrogenase activity. A decrease in absorption of hydrogenase at 400 nm in the presence of these metal ions is indicative of the destruction of the FeS cluster in the enzyme.
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PMID:Influence of metal ions on hydrogenase from the purple sulfur bacterium Thiocapsa roseopersicina. 1111 45

Cadmium and lead metals deposited on CdS particles are shown to act as substrates--electron donors for enzymes, hydrogenase from Thiocapsa roseopersicina (HG), NAD-dependent hydrogenase from Alcaligenes eutrophus (NLH), and ferredoxin:NADP oxidoreductase (FNR) from Chlorella in the formation of hydrogen, NADH and NADPH, respectively. Adsorption of the enzyme on the surface of the metallized CdS particle is required for enzymatic oxidation of metal. The maximum rates for the formation of hydrogen and NADH catalyzed by hydrogenase and NAD-dependent hydrogenase with metals as electron donors are comparable with the rates obtained for these enzymes using soluble substrates. Kinetic analysis of the enzymatic oxidation of cadmium metal has revealed that the rate decreases mainly due to the formation of a solid product, which is supposed to be Cd(OH)2. The deceleration of lead oxidation catalyzed by hydrogenase proceeds at the expense of the inhibitory effect of the formed Pb2+. The enzymatic oxidation of electrochemically prepared cadmium metal is also shown. Based on these results, a new mechanism of action of the enzymes involved in anaerobic biocorrosion is proposed. By this mechanism, the enzyme accelerates the process of metal dissolution through a mediatorless catalysis of the reduction of the enzyme substrate.
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PMID:Enzymatic oxidation of cadmium and lead metals photodeposited on cadmium sulfide. 1120 26

The fidelity of metal incorporation into the active center of hydrogenase 3 from Escherichia coli was studied by analyzing the inhibition of the maturation pathway by zinc and other transition metals. Hydrogenase maturation of wild-type cells was significantly affected only by concentrations of zinc or cadmium higher than 200 microM, whereas a mutant with a lesion in the nickel uptake system displayed a total blockade of the proteolytic processing of the precursor form into the mature form of the large subunit after growth in the presence of 10 microM Zn(2+). The precursor could not be processed in vitro by the maturation endopeptidase even in the presence of an excess of nickel ions. Evidence is presented that zinc does not interfere with the incorporation of iron into the metal center. Precursor of the large subunit accumulated in nickel proficient cells formed a transient substrate complex with the cognate endoprotease HycI whereas that of zinc-supplemented cells did not. The results show that zinc can intrude the nickel-dependent maturation pathway only when nickel uptake is blocked. Under this condition zinc appears to be incorporated at the nickel site of the large subunit and delivers a precursor not amenable to proteolytic processing since the interaction with the endoprotease is blocked.
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PMID:Fidelity of metal insertion into hydrogenases. 1141 15

Some properties of a hydrogenase from the recently isolated phototrophic sulfur bacterium Lamprobacter modestohalophilus strain Syvash and its resistance to a number of inactivating factors have been investigated. The enzyme consists of two subunits, 64 and 30 kD; pI = 4.5. The optimal pH was 8.5-9.5 for hydrogen uptake and 4.0 for H2 evolution. Hydrogenase preparations were resistant to the effects of O2, CO, and temperature, revealing high stability under storage. A considerable inactivation of the enzyme was observed at temperatures above 80 degrees C; the temperature optimum of methyl viologen reduction by H2 was 85 degrees C. Inhibitory effects of Ni2+, Cd2+, and Mg2+ on the hydrogenase activity were shown to be reversible and competitive with respect to methyl viologen in the hydrogen oxidation reaction.
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PMID:Properties of stable hydrogenase from the purple sulfur bacterium Lamprobacter modestohalophilus. 1500 Jun 82

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

Individual gene-targeted hpn and hpn-like mutants and a mutant with mutations in both hpn genes were more sensitive to nickel, cobalt, and cadmium toxicity than was the parent strain, with the hpn-like strain showing the most metal sensitivity of the two individual His-rich protein mutants. The mutant strains contained up to eightfold more urease activity than the parent under nickel-deficient conditions, and the parent strain was able to achieve mutant strain activity levels by nickel supplementation. The mutants contained 3- to 4-fold more and the double mutant about 10-fold more Ni associated with their total urease pools, even though all of the strains expressed similar levels of total urease protein. Hydrogenase activities in the mutants were like those in the parent strain; thus, hydrogenase is fully activated under nickel-deficient conditions. The histidine-rich proteins appear to compete with the Ni-dependent urease maturation machinery under low-nickel conditions. Upon lowering the pH of the growth medium from 7.3 to 5, the wild-type urease activity increased threefold, but the activity in the three mutant strains was relatively unaffected. This pH effect was attributed to a nickel storage role for the His-rich proteins. Under low-nickel conditions, the addition of a nickel chelator did not significantly affect the urease activity of the wild type but decreased the activity of all of the mutants, supporting a role for the His-rich proteins as Ni reservoirs. These nickel reservoirs significantly impact the active urease activities achieved. The His-rich proteins play dual roles, as Ni storage and as metal detoxification proteins, depending on the exogenous nickel levels.
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PMID:Roles of His-rich hpn and hpn-like proteins in Helicobacter pylori nickel physiology. 1738 82


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