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)

Different species of methanogenic bacteria growing on CO(2) and H(2) were shown to remove CO added to the gas phase. Rates up to 0.2 mumol of CO depleted/min per 10 ml of culture containing approximately 7 mg of cells (wet weight) were observed. Methanobacterium thermoautotrophicum was selected for further study based on its ability to grow rapidly on a completely mineral medium. This species used CO as the sole energy source by disproportionating CO to CO(2) and CH(4) according to the following equation: 4CO + 2H(2)O --> 1CH(4) + 3CO(2). However, growth was slight, and the growth rate on CO was only 1% of that observed on H(2)/CO(2). Growth only occurred with CO concentrations in the gas phase of lower than 50%. Growth on CO agrees with the finding that cell-free extracts of M. thermoautotrophicum contained both an active factor 420 (F(420))-dependent hydrogenase (7.7 mumol/min per mg of protein at 35 degrees C) and a CO-dehydrogenating enzyme (0.2 mumol/min per mg of protein at 35 degrees C) that catalyzed the reduction of F(420) with CO. The properties of the CO-dehydrogenating enzyme are described. In addition to F(420), viologen dyes were effective electron acceptors for the enzyme. The apparent K(m) for CO was higher than 1 mM. The reaction rate increased with increasing pH and displayed an inflection point at pH 6.7. The temperature dependence of the reaction rate followed the Arrhenius equation with an activation energy (DeltaHdouble dagger) of 14.1 kcal/mol (59.0 kJ/mol). The CO dehydrogenase activity was reversibly inactivated by low concentrations of cyanide (2 muM) and was very sensitive to inactivation by oxygen. Carbon monoxide dehydrogenase of M. thermoautotrophicum exhibited several characteristic properties found for the enzyme of Clostridium pasteurianum but differed mainly in that the clostridial enzyme did not utilize F(420) as the electron acceptor.
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PMID:Carbon monoxide oxidation by methanogenic bacteria. 2 Nov 59

Extracts of aerobically, CO-autotrophically grown cells of Pseudomonas carboxydovorans were shown to catalyze the oxidation of CO to CO(2) in the presence of methylene blue, pyocyanine, thionine, phenazine methosulfate, or toluylene blue under strictly anaerobic conditions. Viologen dyes and NAD(P)(+) were ineffective as electron acceptors. The same extracts catalyzed the oxidation of formate and of hydrogen gas; the spectrum of electron acceptors was identical for the three substrates, CO, formate, and H(2). The CO- and the formate-oxidizing activities were found to be soluble enzymes, whereas hydrogenase was membrane bound exclusively. The rates of oxidation of CO, formate, and H(2) were measured spectrophotometrically following the reduction of methylene blue. The rate of carbon monoxide oxidation followed simple Michaelis-Menten kinetics; the apparent K(m) for CO was 45 muM. The reaction rate was maximal at pH 7.0, and the temperature dependence followed the Arrhenius equation with an activation energy (DeltaH(0)) of 35.9 kJ/mol (8.6 kcal/mol). Neither free formate nor hydrogen gas is an intermediate of the CO oxidation reaction. This conclusion is based on the differential sensitivity of the activities of formate dehydrogenase, hydrogenase, and CO dehydrogenase to heat, hypophosphite, chlorate, cyanide, azide, and fluoride as well as on the failure to trap free formate or hydrogen gas in coupled optical assays. These results support the following equation for CO oxidation in P. carboxydovorans: CO + H(2)O --> CO(2) + 2 H(+) + 2e(-) The CO-oxidizing activity of P. carboxydovorans differed from that of Clostridium pasteurianum by not reducing viologen dyes and by a pH optimum curve that did not show an inflection point.
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PMID:Oxidation of carbon monoxide in cell extracts of Pseudomonas carboxydovorans. 3 64

Mechanical disruption of cells of Methanobacterium strain G2R resulted in a 78-fold increase in the specific activity of the hydrogenase as measured by the benzyl viologen reduction assay. Approximately 50% of the activity in disrupted cells was associated with the particulate fraction. Between 69 and 85% of the particulate hydrogenase was released by treatment with the detergents Triton X-100, deoxycholate, and octyl-beta-d-glucopyranoside. The relative electrophoretic mobilities of the soluble hydrogenases were identical, indicating that G2R possessed a single electrophoretically distinct hydrogenase. The particulate enzyme was inactivated by oxygen and could be reactivated with dithionite or glucose plus glucose oxidase. The enzyme had a pH optimum of 8.5 and resisted heating at 52 but not 77 degrees C. A number of nonspecific dyes, flavin adenine dinucleotide, and riboflavin 5'-phosphate were effective electron acceptors; oxidized nicotinamide adenine dinucleotide, nicotinamide adenine dinucleotide phosphate, and factor 420 were apparently not reduced. Hydrogenase activity was inhibited by p-hydroxymercuribenzoate, cyanide, chloroform, and chloramphenicol. The molecular weight of the solubilized enzyme was 900,000, with subunits of molecular weights 38,500, 50,700, and approximately 80,000. It is suggested that, in intact cells of G2R, the large hydrogenase complex is loosely bound to the cell wall or membrane.
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PMID:Solubilization and properties of a particulate hydrogenase from Methanobacterium strain G2R. 3 36

The properties of purified hydrogenase [EC 1.12.2.1] solubilized from particulate fraction of sonicated Desulfovibrio vulgaris cells are described. The enzyme was a brownish iron-sulfur protein of molecular weight 89,000, composed of two different subunits (mol. wt.: 28,000 and 59,000), and it contained 7-9 iron atoms and 7-8 labile sulfide ions. Molybdenum was not detected in the preparation. The absorption spectrum of the enzyme was characteristic of iron-sulfur proteins. The millimolar absorbance coefficients of the enzyme were about 164 at 280nm, and 47 at 400nm. The absorption spectrum of the enzyme in the visible region changed upon incubating the enzyme under H2 in the presence of cytochrome c3, but not in its absence. This spectral change was due to the reduction of the enzyme. The absorbance ratio at 400nm of the reduced and the oxidized forms of the enzyme was 0.66. The activity of the enzyme was hardly affected by metal-complexing agents such as cyanide, azide, 1,10-phenanthroline, etc., except for CO, which was a strong inhibitor of the enzyme. The activity was inhibited by SH-reagents such as p-chloromercuribenzenesulfonate. The enzyme was significantly resistant to urea, but susceptible to sodium dodecyl sulfate. These properties were very similar to those of clostridial hydrogenase [EC 1.12.7.1], in spite of differences in the acceptor specificity and subunit structure.
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PMID:Properties of purified hydrogenase from the particulate fraction of Desulfovibrio vulgaris, Miyazaki. 18 72

EPR spectroscopic and chemical analyses of spinach nitrite reductase show that the enzyme contains one reducible iron-sulfur center, and one site for binding either cyanide or nitrite, per siroheme. The heme is nearly all in the high spin ferric state in the enzyme as isolated. The extinction coefficient of the enzyme has been revised to E386 = 7.6 X 10(4) cm-1 (M heme)-1. The iron-sulfur center is reduced with difficulty by agents such as reduced methyl viologen (equilibrated with 1 atm of H2 at pH 7.7 in the presence of hydrogenase) or dithionite. Complexation of the enzyme with CO (a known ligand for nitrite reductase heme) markedly increases the reducibility of the iron-sulfur center. New chemical analyses and reinterpretation of previous data show that the enzyme contains 6 mol of iron and 4 mol of acid-labile S2-/mol of siroheme. The EPR spectrum of reduced nitrite reductase in 80% dimethyl sulfoxide establishes clearly that the enzyme contains a tetranuclear iron-sulfur (Fe4S4) center. The ferriheme and Fe4S4 centers are reduced at similar rates (k = 3 to 4 s-1) by dithionite. The dithionite-reduced Fe4S4 center is rapidly (k = 100 s-1) reoxidized by nitrite. These results indicate a role for the Fe4S4 center in catalysis.
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PMID:Identification of the iron-sulfur center of spinach ferredoxin-nitrite reductase as a tetranuclear center, and preliminary EPR studies of mechanism. 21 90

An investigation was made of certain factors involved in the formation of hydrogen gas, both in an anaerobic environment (argon) and in air, by the blue-green alga Anabaena cylindrica. The alga had not been previously adapted under hydrogen gas and hence the hydrogen evolution occurred entirely within the nitrogen-fixing heterocyst cells; organisms grown in a fixed nitrogen source, and which were therefore devoid of heterocysts, did not produce hydrogen under these conditions. Use of the inhibitor dichlorophenyl-dimethyl urea showed that hydrogen formation was directly dependent on photosystem I and only indirectly dependent on photosystem II, consistent with heterocysts being the site of hydrogen formation. The uncouplers carbonyl cyanide chlorophenyl hydrazone and dinitrophenol almost completely inhibited hydrogen formation, indicating that the process occurs almost entirely via the adenosine 5'-triphosphate-dependent nitrogenase. Salicylaldoxime also inhibited hydrogen formation, again illustrating the necessity of photophosphorylation. Whereas hydrogen formation could usually only be observed in anaerobic, dinitrogen-free environments, incubation in the presence of the dinitrogen-fixing inhibitor carbon monoxide plus the hydrogenase inhibitor acetylene resulted in significant formation of hydrogen even in air. Hydrogen formation was studied in batch cultures as a function of age of the cultures and also as a function of culture concentration, in both cases the cultures being harvested in logarithmic growth. Hydrogen evolution (and acetylene-reducing activity) exhibited a distinct maximum with respect to the age of the cultures. Finally, the levels of the protective enzyme, superoxide dismutase, were measured in heterocyst and vegetative cell fractions of the organism; the level was twice as high in heterocyst cells (2.3 units/mg of protein) as in vegetative cells (1.1 units/mg of protein). A simple procedure for isolating heterocyst cells is described.
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PMID:Anaerobic and aerobic hydrogen gas formation by the blue-green alga Anabaena cylindrica. 41 67

Thiosulfate and sulfide were detected in the sulfite reductase reaction catalyzed by a cell-free extract of photoautotrophically grown Chromatium vinosum. Hydrogen was consumed upon addition of sulfite to the extract in the presence of hydrogenase and methylviologen. Hydrogen uptake proceeded biphasically. During the first phase, thiosulfate and sulfide were formed concomitant with the decrease in sulfite. After the disappearance of sulfite, hydrogen was consumed with reduced velocity and sulfide accumulated as the final product with the total consumption of three mol of hydrogen per mol of sulfite. The molecular weight of a major sulfite reductase was estimated to be about 180,000 by the polyacrylamide disc electrophoresis method using enzyme staining. Arsenite. EDTA, alpha,alpha'-dipyridyl, cyanide, or azide did not inhibit the activity at the concentration of 1 mM. The activity was present in the soluble fraction and was stable at --20 degrees C.
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PMID:Chromatium sulfite reductase. I. Characterization of thiosulfate-forming activity at the cell extract level. 73 Jul 52

A novel hydrogenase has recently been found in methanogenic archaea. It catalyzes the reversible dehydrogenation of methylenetetrahydromethanopterin (CH2 = H4MPT) to methenyltetrahydromethanopterin (CH identical to H4MPT+) and H2 and was therefore named H2-forming methylenetetrahydromethanopterin dehydrogenase. The hydrogenase, which is composed of only one polypeptide with an apparent molecular mass of 43 kDa, does not mediate the reduction of viologen dyes with either H2 or CH2 = H4MPT. We report here that the purified enzyme from Methanobacterium thermoautotrophicum exhibits the following other unique properties: (a) the colorless protein with a specific activity of 2000 U/mg (Vmax) did not contain iron-sulfur clusters, nickel, or flavins; (b) the activity was not inhibited by carbon monoxide, acetylene, nitrite, cyanide, or azide; (c) the enzyme did not catalyze an isotopic exchange between 3H2 and 1H+; (d) the enzyme catalyzed the reduction of CH identical to H4MPT+ with 3H2 generating [methylene-3H]CH2 = H4MPT; and (e) the primary structure contained at most four conserved cysteines as revealed by a comparison of the DNA-deduced amino acid sequence of the proteins from M. thermoautotrophicum and Methanopyrus kandleri. None of the four cysteines were closely spaced as would be indicative for a (NiFe) hydrogenase or a ferredoxin-type iron-sulfur protein. Properties of the H2-forming methylenetetrahydromethanopterin dehydrogenase from Methanobacterium wolfei are also described indicating that the enzyme from this methanogenic archaeon is very similar to the enzyme from M. thermoautotrophicum with respect both to molecular and catalytic properties.
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PMID:H2-forming methylenetetrahydromethanopterin dehydrogenase, a novel type of hydrogenase without iron-sulfur clusters in methanogenic archaea. 152 40

The reduction potentials of two relatively high-molecular-mass enzymes were determined directly at an edge pyrolytic graphite electrode by using square-wave voltammetry. The equilibrium reduction potential versus standard hydrogen electrode was determined for Clostridium pasteurianum hydrogenase I (E'0 = -377 +/- 10 mV; molecular mass 60 kDa) and Rhodospirillum rubrum carbon monoxide dehydrogenase (E'0 = -418 +/- 7 mV; molecular mass 62 kDa). The reduction potential of each enzyme was pH-independent, and one electron was transferred per redox centre. The reduction potential was determined to be identical for the CO dehydrogenase, semi-apo-(CO dehydrogenase), and CO dehydrogenase with carbonyl sulphide (COS) or cyanide bound. The electron-transferring efficiency of CO dehydrogenase was affected by two inhibitors, COS and cyanide, as indicated by a diminished analytic current.
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PMID:Direct electrochemical studies of hydrogenase and CO dehydrogenase. 163 98

Both nickel-specific transport and nickel transport by a magnesium transporter have been described previously for a variety of nickel-utilizing bacteria. The derepression of hydrogenase activity in Bradyzhizobium japonicum JH and in a gene-directed mutant of strain JH (in an intracellular Ni metabolism locus), strain JHK7, was inhibited by MgSO4. For both strains, Ni2+ uptake was also markedly inhibited by Mg2+, and the Mg(2+)-mediated inhibition could be overcome by high levels of Ni2+ provided in the assay buffer. The results indicate that both B. japonicum strains transport Ni2+ via a high-affinity magnesium transport system. Dixon plots (1/V versus inhibitor) showed that the divalent cations Co2+, Mn2+, and Zn2+, like Mg2+, were competitive inhibitors of Ni2+ uptake. The KiS for nickel uptake inhibition by Mg2+, Co2+, Mn2+, and Zn2+ were 48, 22, 12, and 8 microM, respectively. Cu2+ strongly inhibited Ni2+ uptake, and molybdate inhibited it slightly. Respiratory inhibitors cyanide and azide, the uncoupler carbonyl cyanide m-chlorophenylhydrazone, the ATPase inhibitor N,N'-dicyclohexylcarbodiimide, and ionophores nigericin and valinomycin significantly inhibited short-term (5 min) Ni2+ uptake, showing that Ni2+ uptake in strain JH is energy dependent. Most of these conclusions are quite different from those reported previously for a different B. japonicum strain belonging to a different serogroup.
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PMID:Competitive inhibition of an energy-dependent nickel transport system by divalent cations in Bradyrhizobium japonicum JH. 178 26


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