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)

Under anaerobic conditions, cells of Entamoeba histolytica grown with bacteria produce H2 and acetate while cells grown axenically produce neither. Aerobically, acetate is produced and O2 is consumed by amebae from either type of cells. Centrifuged extracts, 2.4 x 106 x g x min, from both types of cells contain pyruvate synthase (EC 1.2.7.1) and an acetate thiokinase which, together, form a system capable of converting pyruvate to acetate. Pyruvate synthase catalyzes the reaction: pyruvate + CoA leads to CO2 + acetyl-CoA + 2E. Electron acceptors which function with this enzyme are FAD, FMN, riboflavin, ferredoxin, and methyl viologen, but not NAD or NADP. The amebal acetate thiokinase catalyzes the reaction acetyl-CoA + ADP + Pi leads to acetate + ATP + CoA. For this apparently new enzyme we suggest the trivial name acetyl-CoA-synthetase (ADP-forming). Extracts from axenic amebae do not contain hydrogenase, but extracts from cells grown with bacteria do. It is postulated that in bacteria-grown amebae electrons generated at the pyruvate synthase step are utilized anaerobically to produce H2 via the hydrogenase and that the acetyl-CoA is converted to acetate in an energy-conserving step catalyzed by amebal acetyl-CoA synthetase. Aerobically, cells grown under either regimen may utilize the energy-conserving pyruvate-to-acetate pathway since O2 then serves as the ultimate electron acceptor.
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PMID:An energy-conserving pyruvate-to-acetate pathway in Entamoeba histolytica. Pyruvate synthase and a new acetate thiokinase. 1 76

A factor of protein nature, containing pteridines and iron ions was isolated from pea leaves. The compound was shown capable of activating NADP reduction during chloroplasts illumination in the absence of ferredoxin. The compound was termed "NADP-reducing factor" (NRP). Freshly isolated NRF in combination with the protein possessing the NADP-reductase activity, reduces NADP in the dark. The factor accepts the electron from the reaction site of the first photosystem and activates hydrogen liberation in the systems, containing hydrogenase. A possibility of an existence of an additional site of NADP reduction in chloroplasts is discussed.
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PMID:[Participation of the iron-containing pterine-protein complex in NADP reduction and electron transport]. 1 45

1. Superoxide dismutase activity was present in the heterocysts and vegetative cells of Anabaena cylindrica, but was always lower in the heterocysts. 2. No qualitative differences were found in the superoxide dismutase from the two cellular types. 3. Catalase activity was also present in both cellular types. 4. Most of the NADP reductase activity, as assayed with menadione or ferredoxin as electron acceptor, was localized within the heterocysts. 5. Studies on H2 consumption showed that most of the hydrogenase activity was associated with the heterocysts. 6. The results are discussed in terms of the postulate that superoxide dismutase and catalase are involved in the protection of the proton-donating systems participating in N2 fixation and H2 metabolism of heterocysts.
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PMID:Superoxide dismutase and catalase in the protection of the proton-donating systems of nitrogen fixation in the blue-green alga Anabaena cylindrica. 10 Dec 10

1. Anaerobic hydrogenase activity in whole cells and cell-free preparations of H2-induced Anacystis was studied both manometrically and spectrophotometrically in presence of physiological and artificial electron acceptors. 2. Up to 90% of the activity measured in crude extracts were recovered in the chlorophyll-containing membrane fraction after centrifugation (144 000 X g, 3 h). 3. Reduction of methyl viologen, diquat, ferredoxin, nitrite and NADP by the membranes was light dependent while oxidants of more positive redox potential were reduced also in the dark. 4. Evolution of H2 by the membranes was obtained with dithionite and with reduced methyl viologen; the reaction was stimulated by detergents. 5. Both uptake and evolution of H2 were sensitive to O2, CO, and thiolblocking agents. The H2-dependent reductions were inhibited also by the plastoquinone antagonist dibromothymoquinone, while the ferredoxin inhibitor disalicylidenepropanediamine affected the photoreduction of nitrite and NADP only. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea did not inhibit any one of the H2-dependent reactions. 6. The results present evidence for a membrane-bound 'photoreduction' hydrogenase in H2-induced Anacystis. The enzyme apparently initiates a light-driven electron flow from H2 to various low-potential acceptors including endogenous ferredoxin.
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PMID:Anaerobic hydrogenase activity in Anacystis nidulans. H2-dependent photoreduction and related reactions. 11 79

Purple bacteria Rhodospirillum rubrum and Thiocapsa roseopersicina form two enzymes, hydrogenase and nitrogenase, which participate in hydrogen metabolism. H2 photoproduction in these bacteria is associated mainly or completely with the action of nitrogenase. The soluble and membrane-bound hydrogenases of T. roseopersicina have similar physicochemical properties (mol. weight, subunit composition, N-terminal amino acids, Fe2+ and S2- content, pl. Eo'). In comparison with other hydrogenases the enzyme from R. rubrum and T. roseopersicina evolve H2 with high rate from reduced cytochrome c3, but not from ferredoxins. H2 production and N2 fixation take place in the presence of NAD(P)H. NADP-reductase, ferredoxin and cytochrome c3 participate in this reaction. Possible relationships between hydrogenase-nitrogenase in the metabolism of molecular hydrogen are discussed.
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PMID:Relationships in hydrogen metabolism between hydrogenase and nitrogenase in phototrophic bacteria. 20 59

Cell-free extracts of Methanobacterium thermoautotrophicum were found to contain high activities of the following oxidoreductases (at 60 degrees C): pyruvate dehydrogenase (coenzyme A acetylating), 275 nmol/min per mg of protein; alpha-ketoglutarate dehydrogenase (coenzyme A acylating), 100 nmol/min per mg; fumarate reductase, 360 nmol/min per mg; malate dehydrogenase, 240 nmol/min per mg; and glyceraldehyde-3-phosphate dehydrogenase, 100 nmol/min per mg. The kinetic properties (apparent V(max) and K(M) values), pH optimum, temperature dependence of the rate, and specificity for electron acceptors/donors of the different oxidoreductases were examined. Pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase were shown to be two separate enzymes specific for factor 420 rather than for nicotinamide adenine dinucleotide (NAD), NADP, or ferredoxin as the electron acceptor. Both activities catalyzed the reduction of methyl viologen with the respective alpha-ketoacid and a coenzyme A-dependent exchange between the carboxyl group of the alpha-ketoacid and CO(2). The data indicate that the two enzymes are similar to pyruvate synthase and alpha-ketoglutarate synthase, respectively. Fumarate reductase was found in the soluble cell fraction. This enzyme activity coupled with reduced benzyl viologen as the electron donor, but reduced factor 420, NADH, or NADPH was not effective. The cells did not contain menaquinone, thus excluding this compound as the physiological electron donor for fumarate reduction. NAD was the preferred coenzyme for malate dehydrogenase, whereas NADP was preferred for glyceraldehyde-3-phosphate dehydrogenase. The organism also possessed a factor 420-dependent hydrogenase and a factor 420-linked NADP reductase. The involvement of the described oxidoreductases in cell carbon synthesis is discussed.
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PMID:Oxidoreductases involved in cell carbon synthesis of Methanobacterium thermoautotrophicum. 91 79

The cells of Pseudomonas methylica, strain 2, cultivated in a medium containing methanol, displayed the activity of hydrogenase in the exchange reaction (D2--H2O) and in the absorption of H2 in the presence of methylviologen, azocarmine, methylene blue, and ferricyanide. The rate of H2 utilization was highest in the presence of methylviologen. Cell extracts absorb H2 in the presence of methylviologen, NAD, and NADP, but much faster in the presence of flavin mononucleotide. The bulk of the hydrogenase remains, during centrifugation of the initial cell extract (3,000 g), in the soluble fraction (144,000 g). The absorption of oxygen by the cell suspensions and the incorporation of 14C of formiate into the cells are stimulated by H2. The cells, however, cannot grow in the autotrophic conditions at the account of molecular hydrogen and CO2.
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PMID:[Hydrogenase activity of the methylotroph, Pseudomonas methylica]. 120 95

Highly-purified bidirectional hydrogenase (hydrogenase 1) of Clostridium pasteurianum could rapidly reduce several 2-, 4- and 5-nitroimidazole compounds via an electron carrier-coupled mechanism. Hydrogenase 1 was also shown to reduce a 2-nitroimidazole (misonidazole) and a 4-nitroimidazole in the presence of its required electron carriers including ferredoxin, the flavin coenzymes FAD and FMN, and the low potential electron carrier dyes methyl- and benzyl-viologen. No drug reduction by hydrogenase 1 occurred when any one of these electron carriers was replaced by nicotinamide electron carriers (NAD and NADP), or was omitted from the reaction mixture. The rates of reduction of the nitroimidazole compounds correlated with their one electron reduction potentials at pH 7(E7(1)); the higher the drug's E7(1), the faster its rate of reduction by the enzyme. Reduction rates for the drugs did not correlate with the antibacterial activity of these compounds against C. pasteurianum, suggesting that other factors are also important in determining the antimicrobial potencies of nitroimidazoles.
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PMID:Reduction of 2-, 4- and 5-nitroimidazole drugs by hydrogenase 1 in Clostridium pasteurianum. 218 Aug 90

The pathway for the anaerobic catabolism of gallic acid by Eubacterium oxidoreducans was studied by using both in vivo and cell-free systems. Cells grown with gallate and crotonate, but with no formate or H2, excreted pyrogallol and phloroglucinol into the medium. Gallate was decarboxylated by crude cell extracts, with pyrogallol as the only detectable product. Whole cells converted pyrogallol to phloroglucinol. A phloroglucinol reductase catalyzed the conversion of phloroglucinol to dihydrophloroglucinol when NADPH was used as the source of electrons. Both formate dehydrogenase (EC 1.2.1.43) and hydrogenase (EC 1.18.99.1) were present in cell extracts of gallate-formate-grown cells. These two enzymes were both NADP linked. Since either H2 or formate is required for cell growth with gallate or phloroglucinol, these results suggest that the oxidation of the reduced substrate may be indirectly linked to the reduction of phloroglucinol. A dihydrophloroglucinol hydrolase was present, which hydrolyzed dihydrophloroglucinol to 3-hydroxy-5-oxohexanoate. This six-carbon ring cleavage product then presumably can be broken down by a series of reactions similar to beta-oxidation. These reactions cleaved the six-carbon acid to 3-hydroxybutyryl-coenzyme A yielding acetate and butyrate as end products. A number of key enzymes involved in beta-oxidation and substrate-level phosphorylation were demonstrated in cell extracts.
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PMID:Metabolism of gallate and phloroglucinol in Eubacterium oxidoreducens via 3-hydroxy-5-oxohexanoate. 357 Nov 53

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


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