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

From enrichment cultures four carbon monoxide utilizing bacteria were isolated; strain OM5 isolated from waste water was studied in detail. The cells are Gram-negative, slightly curved rods, motile by a single subpolarly inserted flagellum. The colonies are smooth, translucent and not slimy. The cells are able to grow autotrophically in mineral medium under an atmosphere of 40% CO, 5% O2 and 55% N2 at a doubling time of 20h (30 degrees C) or of 85% H2, 5% O2 and 10% CO2 at a doubling time of 7h. Heterotrophic growth occurred on organic acids such as acetate(td = 8h), pyruvate(td = 8h), lactate, crotonate, malate, succinate (td = 8h), formate (td = 35h) and glyoxylate as substrates. The enzyme system for carbon monoxide utilization is formed only during growth on CO; hydrogenase is present in cells grown on CO or on H2 + CO2 as well as grown on pyruvate. The rate of oxygen reduction by intact CO-grown cells is 3.7-fold higher in the presence of hydrogen than in the presence of carbon monoxide. During growth the stoichiometry of gas uptake was 6.1 CO + 2.8 O2 + H2O leads to CH2O +5.1 CO2. For the new isolate the name Pseudomonas carboxydovorans (Kistner) comb. nov. has been proposed.
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PMID:Reisolation of the carbon monoxide utilizing hydrogen bacterium Pseudomonas carboxydovorans (Kistner) comb. nov. 69 1

In the analysis of an ethanol-CO(2) enrichment of bacteria from an anaerobic sewage digestor, a strain tentatively identified as Desulfovibrio vulgaris and an H(2)-utilizing methanogen resembling Methanobacterium formicicum were isolated, and they were shown to represent a synergistic association of two bacterial species similar to that previously found between S organism and Methanobacterium strain MOH isolated from Methanobacillus omelianskii. In lowsulfate media, the desulfovibrio produced acetate and H(2) from ethanol and acetate, H(2), and, presumably, CO(2) from lactate; but growth was slight and little of the energy source was catabolized unless the organism was combined with an H(2)-utilizing methanogenic bacterium. The type strains of D. vulgaris and Desulfovibrio desulfuricans carried out the same type of synergistic growth with methanogens. In mixtures of desulfovibrio and strain MOH growing on ethanol, lactate, or pyruvate, diminution of methane produced was stoichiometric with the moles of sulfate added, and the desulfovibrios grew better with sulfate addition. The energetics of the synergistic associations and of the competition between the methanogenic system and sulfate-reducing system as sinks for electrons generated in the oxidation of organic materials such as ethanol, lactate, and acetate are discussed. It is suggested that lack of availability of H(2) for growth of methanogens is a major factor in suppression of methanogenesis by sulfate in natural ecosystems. The results with these known mixtures of bacteria suggest that hydrogenase-forming, sulfate-reducing bacteria could be active in some methanogenic ecosystems that are low in sulfate.
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PMID:Growth of desulfovibrio in lactate or ethanol media low in sulfate in association with H2-utilizing methanogenic bacteria. 87 75

Two key autotrophic enzyme systems, hydrogenase and ribulose diphosphate carboxylase, were examined in Mycobacterium gordonae and two other chemolithotrophic, scotochromogenic mycobacteria under different cultural conditions. In all three organisms both enzymes were inducible and were produced in significant levels only in the presence of the specific substrate, hydrogen or carbon dioxide. M. gordonae exhibited increased growth rates and yields, indicating mixotrophic growth, in the presence of a number of single organic substrates, including acetate, pyruvate, glucose, fructose, and glycerol. In contrast to other aerobic hydrogen autotrophs, the presence of either acetate or pyruvate did not repress ribulose diphosphate carboxylase, and mixotrophic growth was rapid with these substrates. In the absence of carbon dioxide, growth in glycerol medium under an atmosphere of hydrogen and oxygen was severely inhibited, even with cells preadapted to heterotrophic growth on glycerol. Cyclic adenosine monophosphate was not effective in inducing hydrogenase or carboxylase in heterotrophic, mixotrophic, or hydrogen-inhibited cultures.
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PMID:Hydrogenase and ribulose diphosphate carboxylase during autotrophic, heterotrophic, and mixotrophic growth of scotochromogenic mycobacteria. 95 16

The microaerophilic protozoon Trichomonas vaginals responds to extracellular changes in oxygen concentration: acetate, lactate, ethanol, H2 and CO2 formation, as well as glucose-depletion rates, are affected. All these variables except ethanol production rates, also differed between clinically metronidazole-sensitive (1910) and resistant (IR78 and CDC85) strains. Most interesting were the greatly increased glucose-scavenging rates of resistant isolates and their low specific activities of hydrogenase and H2 formation rates by comparison with the metronidazole-sensitive strain. Results suggest that all three strains of this parasite are well adapted to the O2 levels prevailing in situ (13-56 microM). Thus, vaginal oxygen tensions have more pronounced effects on the balances of fermentation products in the resistant strains, and results indicate that these strains may then use hydrogenosomal pathways to their advantage.
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PMID:Influence of oxygen on the fermentative metabolism of metronidazole-sensitive and resistant strains of Trichomonas vaginalis. 147 4

Spirochaeta thermophila RI 19.B1 (DSM 6192) fermented glucose to lactate, acetate, CO2, and H2 with concomitant formation of cell material. The cell dry mass yield was 20.0 g/mol of glucose. From the fermentation balance data and knowledge of the fermentation pathway, a YATP of 9.22 g of dry mass per mol of ATP was calculated for pH-uncontrolled batch-culture growth on glucose in a mineral medium. Measurement of enzyme activities in glucose-grown cells revealed that glucose was taken up by a permease and then subjected to ATP-dependent phosphorylation by a hexokinase. Glucose-6-phosphate was further metabolized to pyruvate through the Embden-Meyerhof-Parnas pathway. The phosphoryl donor for phosphofructokinase activity was PPi rather than ATP. This was also found for the type strain of S. thermophila, Z-1203 (DSM 6578). PPi was probably formed by pyrophosphoroclastic cleavage of ATP, with recovery of the resultant AMP by the activity of adenylate kinase. All other measured kinase activities utilized ATP as the phosphoryl donor. Pyruvate was further metabolized to acetyl coenzyme A with concomitant production of H2 and CO2 by pyruvate synthase. Lactate was also produced from pyruvate by a fructose-1,6-diphosphate-insensitive lactate dehydrogenase. Evidence was obtained for the transfer of reducing equivalents from the glycolytic pathway to hydrogenase to produce H2. No formate dehydrogenase or significant ethanol-producing enzyme activities were detected.
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PMID:Glucose catabolism by Spirochaeta thermophila RI 19.B1. 155 64

To establish the function of the periplasmic Fe-only hydrogenase in the anaerobic sulfate reducer Desulfovibrio vulgaris (Hildenborough), derivatives with a reduced content of this enzyme were constructed by introduction of a plasmid that directs the synthesis of antisense RNA complementary to hydrogenase mRNA. It was demonstrated that the antisense RNA technique allowed specific suppression of the synthesis of this hydrogenase in D. vulgaris by decreasing the amount of hydrogenase mRNA but did not result in the complete elimination of the enzyme, as is usual with most conventional mutagenesis techniques. The hydrogenase content in these antisense RNA-producing D. vulgaris clones was two- to threefold lower than in the parental strain when the strains were grown in batch cultures with lactate as a substrate and sulfate as a terminal electron acceptor. Under these conditions, several differences in growth parameters were measured between the hydrogenase-suppressed clones and wild-type D. vulgaris: growth rates of the clones decreased two- to threefold, and at excess lactate, growth yields were reduced by 20%. Furthermore, the amount of hydrogen measured in the culture headspaces was reduced three- to fivefold for the clones. These observations indicate that this hydrogenase has an important function during growth on lactate and is involved in hydrogen production from protons and electrons originating from at least one of the two oxidation reactions in the conversion of lactate to acetate. The implications for the energy metabolism of D. vulgaris are discussed.
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PMID:Reduction of the amount of periplasmic hydrogenase in Desulfovibrio vulgaris (Hildenborough) with antisense RNA: direct evidence for an important role of this hydrogenase in lactate metabolism. 171 Oct 25

The effects of O2 and CO2 on the growth in culture of Trichomonas vaginalis strain C1-NIH were investigated. Growth under pre-purified N2 in the absence of CO2 supplementation gave a doubling time of 4.4 h; when traces of O2 (less than 0.25 microM) were present, the doubling time was 3.5 h. Organisms grew most rapidly (doubling time 2.3 h) with traces of O2 (less than 0.25 microM) and with the CO2 level controlled at 5 mM. The balance of fermentation products from maltose was greatly influenced by supplied gases. Under strictly anaerobic conditions at 5 mM CO2, equimolar glycerol and lactate accounted for more than 95% of the measured products, whereas lower CO2 increased acetate production. Under microaerobic conditions (O2 less than 0.25 microM) acetate was the major product when CO2 was limited to that evolved endogenously; again 5 mM CO2 favoured glycerol and lactate production. Activities of key enzymes measured in cell-free extracts (pyruvate:ferredoxin oxidoreductase, hydrogenase, glycerol kinase, malate dehydrogenase (decarboxylating) and lactate dehydrogenase) altered with growth conditions commensurately with observed changes in metabolic flux patterns. These results suggest that T. vaginalis is optimally adapted to conditions it experiences in situ in the vagina (traces of O2, high CO2).
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PMID:Trichomonas vaginalis requires traces of oxygen and high concentrations of carbon dioxide for optimal growth. 211 56

Strains of Clostridium thermoaceticum were tested for H2- and CO-dependent growth in a defined medium containing metals, minerals, vitamins, cysteine-sulfide, CO2-bicarbonate, and H2 or CO. Ten of the thirteen strains tested grew at the expense of H2 and CO, and C. thermoaceticum ATCC 39073 was chosen for further study. The doubling times for H2- and CO-dependent growth under chemolithotrophic conditions (the defined medium with nicotinic acid as sole essential vitamin and sulfide as sole reducer) were 25 and 10 h, respectively. Product stiochiometries for chemolithotrophic cultures approximated: 4.1H2 + 2.4CO2----CH3COOH + 0.1 cell C + 0.3 unrecovered C and 6.8CO----CH3COOH + 3.5CO2 + 0.4 cell C + 0.9 unrecovered C. H2-dependent growth produced significantly higher acetate concentrations per unit of biomass synthesized than did CO- or glucose-dependent growth. In contrast, the doubling time for H2-dependent growth under chemolithotrophic conditions (the defined medium without vitamins and sulfide as sole reducer) by Acetogenium kivui ATCC 33488 was 2.7 h; as a sole energy source, CO was not growth supportive for A. kivui. The YH2 values for A. kivui and C. thermoaceticum were 0.91 and 0.46 g of cell dry weight per mol of H2 consumed, respectively; the YCO value for C. thermoaceticum was 1.28 g of cell dry weight per mol of CO consumed. The specific activities of hydrogenase and CO dehydrogenase in both acetogens were influenced by the energy source utilized for growth and were significantly lower in C. thermoaceticum than in A. kivui. With extracts of H2-cultivated cells and benzyl viologen as electron acceptor, the Vmax values for hydrogenase from C. thermoaceticum and A. kivui were 155.7 and 1,670 micromoles of H2 oxidized per min mg of protein, respectively; the Vmax values for CO dehydrogenase from C. thermoaceticum and A. kivui were 90.6 and 2,973 micromoles of CO oxidized per min per mg of protein, respectively.
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PMID:Characterization of the H2- and CO-dependent chemolithotrophic potentials of the acetogens Clostridium thermoaceticum and Acetogenium kivui. 237 65

Fermenting anaerobic cultures of Escherichia coli were observed by the nonintrusive technique of in vivo, whole-culture nuclear magnetic resonance. Fermentation balances were calculated for hexoses, pentoses, sugar alcohols, and sugar acids. Substrates more reduced than glucose yielded more of the highly reduced fermentation product ethanol, whereas more-oxidized substrates produced more of the less-reduced fermentation product acetate. These relationships were made more obvious by the introduction of ldhA mutations, which abolished lactate production, and delta frd mutations, which eliminated succinate. When grown anaerobically on sugar alcohols such as sorbitol, E. coli produced ethanol in excess of the amount calculated by the standard fermentation pathways. Reducing equivalents must be recycled from formate to account for this excess of ethanol. In mutants deficient in hydrogenase (hydB), ethanol production from sorbitol was greatly decreased, implying that hydrogen gas released from formate by the formate-hydrogen lyase system may be partially recycled, in the wild type, to increase the yield of the highly reduced fermentation product ethanol.
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PMID:Anaerobic fermentation balance of Escherichia coli as observed by in vivo nuclear magnetic resonance spectroscopy. 268 Nov 56


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