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)

The hydrogenase from D. desulfuricans, when isolated in air, had a low activity in the hydrogen-methyl viologen reductase assay, and no activity in the hydrogen-methylene blue reductase assay. The activity increased markedly during incubation under hydrogen. This process is interpreted in terms of conversion of the enzyme from a relatively inactive Unready state to the Active state. Oxidation by dichloro-indophenol caused conversion to a state in which the hydrogen-uptake activity to methyl viologen was preserved, but hydrogen-methylene blue activity was not. This form is termed the Ready state. This behaviour resembles that of the hydrogenase of Desulfovibrio gigas and thus may be a widespread property of this class of hydrogenases. The electron-spin-resonance spectra of the D. desulfuricans enzyme showed the presence of [3Fe-xS] and [4Fe-4S] clusters. Spectra were also observed in the various states of activation of the enzyme. In these respects, the hydrogenase of D. desulfuricans resembles that from D. gigas, although the latter may have an additional iron-sulphur cluster.
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PMID:Activation and deactivation of the membrane-bound hydrogenase from Desulfovibrio desulfuricans, Norway strain. 301 48

Hydrogenase from Escherichia coli exhibited low activity when assayed for hydrogen:methyl viologen reductase activity and no activity when assayed for hydrogen-uptake activity with acceptors of high redox potential (dichloroindophenol, methylene blue). Nor did the enzyme as isolated catalyse proton-tritium exchange activity. Incubation under hydrogen resulted in an increase in hydrogen-uptake activity with methyl viologen and the appearance of hydrogen-uptake activity with dichloroindophenol and methylene blue. Following such treatment, the enzyme also readily catalysed isotope exchange. This process is interpreted as the conversion of the hydrogenase from an inactive 'unready' state to an 'active' state. Oxidation of active hydrogenase with dichloroindophenol caused conversion to a state resembling that of the enzyme as isolated but capable of more rapid activation under reducing conditions. This form is termed the 'ready' state. Such interconversions have been reported for hydrogenases from Desulfovibrio gigas and D. desulfuricans, and the possibility that they constitute a regulatory mechanism suggested.
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PMID:Reversible activation of hydrogenase from Escherichia coli. 329 95

When grown on formate, formate-CO, and methanol-CO, Butyribacterium methylotrophicum contained high levels of tetrahydrofolate (H4folate) and required enzymes, carbon monoxide dehydrogenase, formate dehydrogenase, and hydrogenase. The activities of methylene-H4folate reductase were comparable to other H4 folate activities (which ranged from 0.55 to 9.28 mumol/min per mg of protein) when measured by an improved procedure. The H4folate activities in formate-grown cells were twice those found in formate-CO-grown cells. This result correlated with a growth yield on formate that was one-half that on formate-CO. The stoichiometry of the formyl-H4folate synthetase reaction was 1 mol of ATP per 1 mol of formate. The methylene-H4folate dehydrogenase was NAD+ dependent. We conclude that B. methylotrophicum utilizes these enzymes in homoacetogenic catabolism.
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PMID:Catabolic enzymes of the acetogen Butyribacterium methylotrophicum grown on single-carbon substrates. 331 88

The metabolic and enzymatic bases for growth tolerance to ethanol (4%) and H2 (2 atm [1 atm = 101.29 kPa]) fermentation products in Clostridium thermohydrosulfuricum were compared in a sensitive wild-type strain and an insensitive alcohol-adapted strain. In the wild-type strain, ethanol (4%) and H2 (2 atm) inhibited glucose but not pyruvate fermentation parameters (growth and end product formation). Inhibition of glucose fermentation by ethanol (4%) in the wild-type strain was reversed by addition of acetone (1%), which lowered H2 and ethanol production while increasing isopropanol and acetate production. Pulsing cells grown in continuous culture on glucose with 5% ethanol or 1 atm of H2 significantly raised the NADH/NAD ratio in the wild-type strain but not in the alcohol-adapted strain. Analysis of key oxidoreductases demonstrated that the alcohol-adapted strain lacked detectable levels of reduced ferredoxin-linked NAD reductase and NAD-linked alcohol dehydrogenase activities which were present in the wild-type strain. Differences in the glucose fermentation product ratios of the two strains were related to differences in lactate dehydrogenase and hydrogenase levels and sensitivity of glyceraldehyde 3-phosphate dehydrogenase activity to NADH inhibition. A biochemical model is proposed which describes a common enzymatic mechanism for growth tolerance of thermoanaerobes to moderate concentrations of both ethanol and hydrogen.
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PMID:Ethanol production by thermophilic bacteria: biochemical basis for ethanol and hydrogen tolerance in Clostridium thermohydrosulfuricum. 337 83

Methanogens catalyze the hydrogen-dependent eight-electron reduction of carbon dioxide to methane. Two of the key catalysts in the eight-electron reduction pathway are the nickel-containing enzymes F420-reducing hydrogenase and methyl reductase. In the present study, the structures of these archaebacterial enzymes from Methanobacterium thermoautotrophicum delta H have been determined by electron microscopy. By negative stain techniques, F420 hydrogenase was found to be a ring structure with a diameter of 15.7 nm and an inner channel 4 nm in diameter. Shadow-casting experiments demonstrated that the rings were 8.5 nm deep, indicating a holoenzyme molecular weight of 8.0 X 10(5). Methyl reductase appeared to be an oligomeric complex of dimensions 8.5 by 9 by 11 nm, with a central stain-penetrating region. The morphology and known subunit composition suggest a model in which the subunits are arranged as an eclipsed pair of open trimers. Methyl reductase was also found in the form of larger aggregates and in paracrystalline arrays derived from highly concentrated solutions. The extremely large size of F420 hydrogenase and the methyl reductase supramolecular assemblies may have relevance in vivo in the construction of multiprotein arrays that function in methane biogenesis.
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PMID:Electron microscopy of nickel-containing methanogenic enzymes: methyl reductase and F420-reducing hydrogenase. 380 76

Reduction of 7,8-didemethyl-8-hydroxy-[5-2H]-5-deazariboflavin by the selenium-containing hydrogenase from Methanococcus vannielii gave a C-5 chirally labeled 1,5-dihydro derivative. The absolute configuration of the chiral label was shown to be (R) by comparison of the chemically degraded product with authentic samples of known absolute configurations. Therefore, the steric course of the enzymic reactions involving the 8-hydroxy-5-deazaflavin cofactor can be defined as follows: (a) reduction occurs on the si face of the 5-deazaflavin molecule; (b) oxidation proceeds by the abstraction of the pro-S hydrogen at C-5 of the 1,5-dihydro-5-deazaflavin. Thus, the selenium-containing hydrogenase and 8-hydroxy-5-deazaflavin-dependent NADP+ reductase from M. vannielii are si face specific.
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PMID:Stereochemical studies of a selenium-containing hydrogenase from Methanococcus vannielii: determination of the absolute configuration of C-5 chirally labeled dihydro-8-hydroxy-5-deazaflavin cofactor. 388 57

Clostridium thermosulfurogenes displayed faster growth on either glucose, maltose, or starch than Clostridium thermohydrosulfuricum. Both species grew faster on glucose than on starch or maltose. The fermentation end product ratios were altered based on higher ethanol and lactate yields on starch than on glucose. In C. thermohydrosulfuricum, glucoamylase, pullulanase, and maltase were mainly responsible for conversion of starch and maltose into glucose, which was accumulated by a putative glucose permease. In C. thermosulfurogenes, beta-amylase was primarily responsible for degradation of starch to maltose, which was accumulated by a putative maltose permease and then hydrolyzed by glucoamylase. Regardless of the growth substrate, the rates of glucose, maltose, and starch transformation were higher in C. thermosulfurogenes than in C. thermohydrosulfuricum. Both species had a functional Embden-Meyerhof glycolytic pathway and displayed the following catabolic activities: ferredoxin-linked pyruvate dehydrogenase, acetate kinase, NAD(P)-ethanol dehydrogenase, NAD(P)-ferredoxin oxidoreductase, hydrogenase, and fructose-1,6-diphosphate-activated lactate dehydrogenase. Ferredoxin-NAD reductase activity was higher in C. thermohydrosulfuricum than NADH-ferredoxin oxidase activity, but the former activity was not detectable in C. thermosulfurogenes. Both NAD- and NADP-linked ethanol dehydrogenases were unidirectional in C. thermosulfurogenes but reversible in C. thermohydrosulfuricum. The ratio of hydrogen-producing hydrogenase to hydrogen-consuming hydrogenase was higher in C. thermosulfurogenes. Two biochemical models are proposed to explain the differential saccharide metabolism on the basis of species enzyme differences in relation to specific growth substrates.
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PMID:Differential amylosaccharide metabolism of Clostridium thermosulfurogenes and Clostridium thermohydrosulfuricum. 393 39

To demonstrate the importance of electron siphoning by the metronidazole reductase system from reduced ferredoxin to the mechanism of action of the drug in Clostridium pasteurianum, the effects of the reduction of metronidazole on the phosphoroclastic reaction were studied. Metronidazole concentrations between 0.5 and 5 mM caused a significant increase in acetyl phosphate production by the phosphoroclastic reaction compared to the control system without metronidazole. When this enzymatic reaction was assayed by standard manometric techniques under nitrogen gas, two simultaneous effects of electron siphoning were demonstrated: (i) the electrons from reduced ferredoxin were initially consumed for the reduction of metronidazole instead of being evolved as H2 via the ferredoxin-linked hydrogenase and (ii) phosphoroclastic activity was stimulated, with augmented production of CO2 and acetyl phosphate. This work further supports the notion of preferential scavenging of electrons away from ferredoxin-linked enzymatic reactions by metronidazole reductase(s) in C. pasteurianum.
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PMID:Role of the phosphoroclastic reaction of Clostridium pasteurianum in the reduction of metronidazole. 401 76

Acryloyl-CoA reductase, a presumably previously unknown soluble enzyme, is present in Clostridium kluyveri. It catalyses the reduction of the carbon-carbon double bond of acryloyl-CoA or ethyl vinyl ketone and other alpha, beta-unsaturated carbonyl compounds at the expense of reduced methylviologen. On the basis of a Vmax/Km ratio, which is at least 18 times higher than that for the next best substrate (E)-2-butenoyl-CoA, the enzyme is called acryloyl-CoA reductase. A purity of over 90% was achieved. The apparent molecular mass, as determined by gel chromatography, is 28.4 kDa. Dodecyl sulfate gel electrophoresis shows subunits with a molecular mass of 14.2 kDa. Based on a molecular mass of 28.4 kDa about 1.5 mol FMN have been observed. Less than 0.2 g-atom iron per mol protein were determined. Ferredoxin or flavodoxin seem to be able to carry electrons from hydrogenase to the acryloyl-CoA reductase. The addition of hydrogen to the alpha-carbon of ethyl vinyl ketone occurs from the re-side.
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PMID:Purification and some properties of an acryloyl-CoA reductase of Clostridium kluyveri. 406 66

Several dissimilatory, sulfate-reducing bacteria were isolated from the rumen fluid of sheep fed purified diets containing sulfate. One isolate, strain D, was selected for characterization. This organism is a nonsporeforming, obligately anaerobic, mesophilic, nonmotile, gram-negative, straight rod. Cell-free extracts show absorption maxima for cytochrome c(3) and desulfoviridin, characteristic of Desulfovibrio. Carbohydrates, as a sole carbon source, will support growth. Lactate supports growth in the presence of sulfate, not in its absence, whereas glucose or pyruvate support growth either in the presence or absence of sulfate. The isolate has a deoxyribonucleic acid base composition of 61.2% guanine plus cytosine, which is similar to that of several other species of Desulfovibrio; however, it differs from previously described species in morphology, motility, and carbon source utilization. Cell-free extracts of this bacterium exhibit adenosine 5'-triphosphate-sulfurylase, adenosine-5'-phosphosulfate-reductase, and hydrogenase activity. After incubation of cell-free extracts with adenine 5'-triphosphate and (35)SO(4) (2-), adenosine-5'-phosphosulfate rather than 3'-phosphoadenosine-5'-phosphosulfate was shown to be labeled, indicating that the pathway of sulfate reduction in this organism is similar to that of other dissimilatory sulfate reducers. This is the first report of a Desulfovibrio sp. isolated from the rumen.
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PMID:Sulfate reduction by a Desulfovibrio species isolated from sheep rumen. 447 25


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