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)

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

Two ferredoxins, Fd I and Fd II, were isolated and purified from Desulfovibrio vulgaris Miyazaki. The major component, Fd I, is an iron-sulfur protein of Mr 12,000, composed of two identical subunits. The absorption spectra of Fd I and Fd II have a broad absorption shoulder near 400 nm characteristic of iron-sulfur proteins. The purity index, A400/A280, of Fd I is 0.69, and its millimolar absorption coefficient at 400 nm is 3.73 per Fe. It contains two redox centers with discrete redox behaviors. The amino acid composition and the N-terminal sequence of Fd I are similar to those of Fd III of Desulfovibrio africanus Benghazi and Fd II of Desulfovibrio desulfuricans Norway. Fd I does not serve as an electron carrier for the hydrogenase of D. vulgaris Miyazaki, but it serves as a carrier for pyruvate dehydrogenase of this bacterium. The evolution of H2 from pyruvate was observed by a reconstructed system containing purified hydrogenase, cytochrome C3, Fd I, partially purified pyruvate dehydrogenase, and CoA. The H2-sulfite reducing system can be reconstructed from the purified hydrogenase, cytochrome C3, Fd I and desulfoviridin (sulfite reductase), but the reaction rate is very slow compared to that of the crude extract at the same molar ratio of the components.
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PMID:Purification and characterization of ferredoxin from Desulfovibrio vulgaris Miyazaki. 336 Jul 52

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

S organism, an anaerobic gram-negative rod, which is one of two bacterial species isolated from the culture known as "Methanobacillus omelianskii," ferments ethanol to acetate and H(2). The present study shows that extracts of this organism contain ferredoxin and produce acetate from acetaldehyde via aldehyde: ferredoxin oxidoreductase activity. Electrons generated in the reaction are given off as H(2) by a previously demonstrated ferredoxin-linked hydrogenase system. Extracts were shown to contain good phosphotransacetylase and acetokinase activities, but no mechanism of adenosine triphosphate generation during acetaldehyde conversion to acetate could be detected. No evidence could be obtained for coenzyme A (CoASH) or phosphate requirement or for formation of acetyl CoA or acetyl phosphate.
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PMID:Ferredoxin-dependent conversion of acetaldehyde to acetate and H 2 in extracts of S organism. 455 84

It has been demonstrated that enzymes from Clostridium thermoaceticum catalyze the following reaction in which Fd is ferredoxin and CH3THF is methyltetrahydrofolate. (for formula see text). The system involves hydrogenase, CO dehydrogenase, a methyltransferase, a corrinoid enzyme and other unknown components. Hydrogenase catalyzes the reduction of ferredoxin by H2; CO dehydrogenase then uses the reduced ferredoxin to reduce CO2 to a one-carbon intermediate that combines with CoASH and with a methyl group originating from CH3THF to form acetyl-CoA. It is proposed that these reactions are part of the mechanism which enables certain acetogenic autotrophic bacteria to grow on CO2 and H2.
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PMID:The synthesis of acetyl-CoA by Clostridium thermoaceticum from carbon dioxide, hydrogen, coenzyme A and methyltetrahydrofolate. 642 23

Enzymological studies on the multienzyme acetyl-CoA decarbonylase synthase (ACDS) complex from Methanosarcina barkeri have been conducted in order to identify and characterize physiologically relevant substrates and reactions in acetyl-CoA synthesis and decomposition in methanogens. Whereas previous investigations employed carbon monoxide as substrate and reducing agent for acetyl-CoA synthesis, we discovered that bicarbonate (or CO2) acts as a highly efficient carbonyl group precursor substrate in the presence of either hydrogen or Ti3+.EDTA as reducing agent. In reactions with Ti3+.EDTA, synthesis of acetyl-CoA was strongly dependent on ferredoxin, and in reactions with H2, dependence on ferredoxin was absolute. Two major hydrogenases were resolved from the enzyme complex preparation by HPLC gel filtration. One of these hydrogenases was shown to be active in reconstitution of acetyl-CoA synthesis in CO2-containing reactions with H2 as reducing agent. The hydrogenase active in reconstitution was capable of reducing ferredoxin, but was unreactive toward the 8-hydroxy-5-deazaflavin derivative coenzyme F420. In contrast, the hydrogenase that did not reconstitute acetyl-CoA synthesis was reactive with F420 but was unable to reduce ferredoxin. Further experiments were performed in which the value of the equilibrium constant (Keq) was determined for the reaction: H2 + CO2 + CH3-H4SPt + CoASH <--> acetyl-CoA + H4SPt + H2O, where CH3-H4SPt and H4SPt stand for N5-methyl-tetrahydrosarcinapterin and tetrahydrosarcinapterin, respectively. Keq for this reaction was found to be 2.09 x 10(6) M-1ATMH2-1 at 37 degrees C. Calculations of thermodynamic values for additional, related reactions were made and are discussed.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Substrate and accessory protein requirements and thermodynamics of acetyl-CoA synthesis and cleavage in Methanosarcina barkeri. 771 64

The syntrophically glycolate-fermenting bacterium in the methanogenic binary coculture FlGlyM was isolated in pure culture (strain FlGlyR) with glyoxylate as sole substrate. This strain disproportionated 12 glyoxylate to 7 glycolate, 10 CO2, and 3 hydrogen. Glyoxylate was oxidized via the malyl-CoA pathway. All enzymes of this pathway, i.e. malyl-CoA lyase/malate: CoA ligase, malic enzyme, and pyruvate synthase, were demonstrated in cell-free extracts. Glycolate dehydrogenase, hydrogenase, and ATPase, as well as menaquinones as potential electron carriers, were present in the membranes. Everted membrane vesicles catalyzed hydrogen-dependent glyoxylate reduction to glycolate [86-207 nmol min-1 (mg protein)-1] coupled to ATP synthesis from ADP and Pi [38-82 nmol min-1 (mg protein)-1)]. ATP synthesis was abolished entirely by protonophores or ATPase inhibitors (up to 98 and 94% inhibition, respectively) indicating the involvement of proton-motive force in an electron transport phosphorylation driven by a new glyoxylate respiration with hydrogen as electron donor. Measured reaction rates in vesicle preparations revealed a stoichiometry of ATP formation of 0.2-0.5 ATP per glyoxylate reduced.
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PMID:Electron transport phosphorylation driven by glyoxylate respiration with hydrogen as electron donor in membrane vesicles of a glyoxylate-fermenting bacterium. 776 34

Hyperthermophiles are a recently discovered group of microorganisms that grow at and above 90 degrees C. They currently comprise over 20 different genera, and except for two novel bacteria, all are classified as Archaea. The majority of these organisms are obligately anaerobic heterotrophs that reduce elemental sulfur (S degree) to H2S. The best studied from a biochemical perspective are the archaeon, Pyrococcus furiosus, and the bacterium, Thermotoga maritima, both of which are saccharolytic. P. furiosus is thought to contain a new type of Entner-Doudoroff pathway for the conversion of carbohydrates ultimately to acetate, H2 and CO2. The pathway is independent of nicotinamide nucleotides and involves novel types of ferredoxin-linked oxidoreductases, one of which has tungsten, a rarely used element, as a prosthetic group. The only site of energy conservation is at the level of acetyl CoA, which is the presence of ADP and phosphate is converted to acetate and ATP in a single step. In contrast, T. maritima utilizes a conventional Embden-Meyerhof pathway for sugar oxidation. P. furiosus also utilizes peptides as a sole carbon and energy source. Amino acid oxidation is thought to involve glutamate dehydrogenase together with at least three types of novel ferredoxin-linked oxidoreductases which catalyze the oxidation of 2-ketoglutarate, aryl pyruvates and formaldehyde. One of these enzymes also utilizes tungsten. In P. furiosus, virtually all of the reductant that is generated during the catabolism of both carbohydrates and peptides is channeled to a cytoplasmic hydrogenase. This enzyme is now termed sulhydrogenase, as it reduces both protons to H2 and S degrees (or polysulfide) to H2S. S degrees reduction appears to lead to the conservation of energy in P. furiosus but not in T. maritima, although the mechanism by which this occurs is not known.
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PMID:Biochemical diversity among sulfur-dependent, hyperthermophilic microorganisms. 794 71

In the anaerobic fungus Neocallimastix sp. L2 fermentation of glucose proceeds via the Embden-Meyerhof-Parnas pathway. Enzyme activities leading to the formation of succinate, lactate, ethanol, and formate are associated with the cytoplasmic fraction. The enzymes 'malic enzyme,' NAD(P)H:ferredoxin oxidoreductase, pyruvate:ferredoxin oxidoreductase, hydrogenase, acetate:succinate CoA transferase and succinate thiokinase leading to the formation of H2,CO2, acetate, and ATP are localized in microbodies. Thus, these organelles are identified as hydrogenosomes. In addition, the microbodies contain the O2-scavenging enzymes NADH- and NADPH oxidase, while NAD(P)H peroxidase, catalase, or superoxide dismutase could not be detected. In cell-free extracts from zoospores of Neocallimastix sp. L2 the specific activities of hydrogenosomal enzymes as well as the quantities of these proteins are 2- to 6-fold higher than in mycelium extracts. These findings suggest that hydrogenosomes perform an important role--especially in zoospores--as H2-evolving, ATP-generating and O2-scavenging organelles.
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PMID:Characterization of hydrogenosomes and their role in glucose metabolism of Neocallimastix sp. L2. 825 82

Acidaminococcus fermentans is able to ferment glutamate to ammonia, CO2, acetate, butyrate, and H2. The molecular hydrogen (approximately 10 kPa; E' = -385 mV) stems from NADH generated in the 3-hydroxybutyryl-CoA dehydrogenase reaction (E degrees ' = -240 mV) of the hydroxyglutarate pathway. In contrast to growing cells, which require at least 5 mM Na+, a Na+-dependence of the H2-formation was observed with washed cells. Whereas the optimal glutamate fermentation rate was achieved already at 1 mM Na+, H2 formation commenced only at > 10 mM Na+ and reached maximum rates at 100 mM Na+. The acetate/butyrate ratio thereby increased from 2.0 at 1 mM Na+ to 3.0 at 100 mM Na+. A hydrogenase and an NADH dehydrogenase, both of which were detected in membrane fractions, are components of a model in which electrons, generated by NADH oxidation inside of the cytoplasmic membrane, reduce protons outside of the cytoplasmic membrane. The entire process can be driven by decarboxylation of glutaconyl-CoA, which consumes the protons released by NADH oxidation inside the cell. Hydrogen production commences exactly at those Na+ concentrations at which the electrogenic H+/Na+-antiporter glutaconyl-CoA decarboxylase is converted into a Na+/Na+ exchanger.
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PMID:Sodium ion-dependent hydrogen production in Acidaminococcus fermentans. 892 82


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