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 soluble, NAD+-reducing hydrogenase in intact cells of Alcaligenes eutrophus was inactivated by oxygen when electron donors such as hydrogen or pyruvate were available. The sole presence of either oxygen or oxidizable substrates did not lead to inactivation of the enzyme. Inactivation occurred similarly under autotrophic growth conditions with hydrogen, oxygen and carbon dioxide. The inactivation followed first order reaction kinetics, and the half-life of the enzyme in cells exposed to a gas atmosphere of hydrogen and oxygen (8:2, v/v) at 30 degrees C was 1.5h. The process of inactivation did not require ATP-synthesis. There was no experimental evidence that the inactivation is a reversible process catalyzed by a regulatory protein. The possibility is discussed that the inactivation is due to superoxide radical anions (O2-) produced by the hydrogenase itself.
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PMID:In vivo inactivation of soluble hydrogenase of Alcaligenes eutrophus. 678 48

Mutants defective in chemolithoautotrophic growth (Aut-) have been isolated from Alcaligenes eutrophus strains H16, N9A, G27, and TF93. Spontaneous Aut- mutants were obtained only with strain TF93. Mutants of the other strains were selected after conventional mutagenesis or treatment with mitomycin. Most of the mutants, including the spontaneous Aut- strains, lacked hydrogenase activity (Hox-) but possessed the ability to fix carbon dioxide (Cfx+). Agar mating of A. eutrophus H16 with Hox- mutants of the various strains resulted in transconjugants which had recovered the ability to grow autotrophically and to express activity of hydrogenase as examined by enzymatic and immunochemical analysis. Transfer of hydrogen-oxidizing ability occurred in the absence of a mobilizing plasmid such as Rp4. The transfer frequency was particularly high (ca. 10(-2) per donor) when the spontaneous Hox- mutants of strain TF93 were used as recipients. These strains proved to be plasmid free, whereas donors, transconjugants, and the mutagen-treated Hox- mutants contained a large plasmid (molecular weight, 270 +/- 10 X 10(6) revealed by agarose gel electrophoresis. The results allow the conclusion that A. eutrophus H16 harbors a self-transmissible plasmid designated pHG1, which carries information for hydrogen-oxidizing ability.
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PMID:Naturally occurring genetic transfer of hydrogen-oxidizing ability between strains of Alcaligenes eutrophus. 678 25

Alcaligenes eutrophus did not form the key enzymes of autotrophic metabolism, the soluble and particulate hydrogenases and ribulosebisphosphate carboxylase (RuBPC), during heterotrophic growth on succinate in batch cultures. During succinate-limited growth in a chemostat, high activities of both hydrogenases were observed. With decreasing dilution rate (D) the steady-state hydrogenase activity (H) followed first-order kinetics, expressed as follows: H = Hmax .e-alpha.D. An identical correlation was observed when autotrophic growth in a chemostat was limited by molecular hydrogen. During autotrophic growth under oxygen or carbon dioxide limitation, the activity if the soluble hydrogenase was low. These data suggested that hydrogenase formation depended on the availability of reducing equivalents to the cells. RuBPC activities were not correlated with the hydrogenase activities. During succinate-limited growth, RuBPC appeared at intermediate activities. During autotrophic growth in a carbon dioxide-limited chemostat, RuBPC was highly derepressed. RuBPC activity was not detected in cells that suffered from energy limitation with a surplus of carbon, as in a heterotrophic oxygen-limited chemostat, nor was it detected in cells limited in carbon and energy, as in the case of complete exhaustion of a heterotrophic substrate. From these data I concluded that RuBPC formation in A. eutrophus depends on two conditions, namely, carbon starvation and an excess of reducing equivalents.
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PMID:Depression of hydrogenase during limitation of electron donors and derepression of ribulosebisphosphate carboxylase during carbon limitation of Alcaligenes eutrophus. 679 17

This paper reports for the first time the presence in the anaerobic rumen ciliate Dasytricha ruminantium (Schuberg) of microbody-like organelles, about 0.5 micrometer diameter, with a granular matrix and an equilibrium density of approx. 1.18 g/ml. These organelles can be isolated in a fraction sedimented at 10(5) g-min that contains 67% of the total pyruvate synthase (EC 1.2.7.1), 66% of the hydrogenase (EC 1.18.3.1) and 20% of the lactate dehydrogenase (EC 1.1.1.27). Thus in several respects this fraction is enzymically similar to those containing hydrogenosomes in some other parasitic anaerobic protozoa (the trichomonads). However, in contrast with the hydrogenosomes of trichomonads, the oxygen-tolerant enzyme malate dehydrogenase (decarboxylating) (EC 1.1.1.40) is not particulate, but occurs only in the cytosol. These results enable the proposal of a scheme for the pathway of product formation (acetate, lactate, CO2 and H2) from carbohydrates.
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PMID:Hydrogenosomes in the rumen protozoon Dasytricha ruminantium Schuberg. 680 78

The acetogenic bacterium Clostridium thermoautotrophicum, grown on methanol, glucose, or CO2-H2, contained high levels of corrinoids, formate dehydrogenase, tetrahydrofolate enzymes, carbon monoxide dehydrogenase, and hydrogenase. Cell-free extracts catalyzed pyruvate-dependent formation of acetate from methyltetrahydrofolate. These results suggest that C. thermoautotrophicum synthesizes acetate from CO2 via a formate-tetrahydrofolate-corrinoid pathway.
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PMID:Levels of enzymes involved in the synthesis of acetate from CO2 in Clostridium thermoautotrophicum. 680 50

Hydrogen evolution and consumption by cell and chromatophore suspensions of the photosynthetic bacterium Rhodopseudomonas capsulata was measured with a sensitive and specific mass spectrometric technique which directly monitors dissolved gases. H2 production by nitrogenase was inhibited by acetylene and restored by carbon monoxide. An H2 evolution activity coupled with HD formation and D2 uptake (H-D exchange) was unaffected by C2H2 and CO. Cultures lacking nitrogenase activity also exhibited H-D exchange activity, which was catalyzed by a membrane-bound hydrogenase present in the chromatophores of R. capsulata. A net hydrogen uptake, mediated by hydrogenase, was observed when electron acceptors such as CO2, O2, or ferricyanide were present in the medium.
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PMID:Continuous monitoring, by mass spectrometry, of H2 production and recycling in Rhodopseudomonas capsulata. 700 56

Growth of various bacteria, especially aerobic hydrogen-oxidizing bacteria, in the presence of 2 to 100% (v/v) oxygen in the gas atmosphere was evaluated. The bacterial strains included Alcaligenes eutrophus, A. paradoxus, Aquaspirillum autotrophicum, Arthrobacter spec. strain 11 X, Escherichia coli, Arthrobacter globiformis, Nocardia opaca, N. autotrophica, Paracoccus denitrificans, Pseudomonas facilis, P. putida, and Xanthobacter autotrophicus. Under heterotrophic conditions with fructose or gluconate as substrates neither colony formation on solid medium nor the growth rates in liquid media were drastically impaired by up to 100% oxygen. In contrast, autotrophic growth--with hydrogen, carbon dioxide and up to 80% oxygen in the gas atmosphere--was strongly depressed by high oxygen concentrations. However, only the growth rate, not the viability of the cells, was decreased. Growth retardation was accompanied by a decrease of hydrogenase activity.
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PMID:Oxygen tolerance of strictly aerobic hydrogen-oxidizing bacteria. 704 81

This work investigated the usefulness of chlorate resistance as a method for the selection of nitrate reductase negative (NR-) strains from Rhizobium japonicum (61A76) and evaluated the symbiotic, characteristics of these strains. Chlorate resistent strains were selected from populations seeded on CS 7 agar containing 10 or 20 mM KC10, and incubated in 2% air- 98% N2-CO2 (95:5). Over 200 resistant strains were isolated, 58% of which lacked the dissimilatory nitrate reductase. In 12 selected isolates, some strains had also lost the assimilatory nitrate reductase, but all retained hydrogenase activity. Chlorate resistant strains inoculated to soybean seedlings were equal to or better than the parent strain in terms of nodule mass and acetylene reduction. Those strains lacking both assimilatory and dissimilatory nitrate reductase showed the best symbiotic characteristics, suggesting that chlorate resistance in R. japonicum could be a useful method for the selection of strains with superiod nitrogen-fixing characteristics.
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PMID:Free-living and symbiotic characteristics of chlorate resistant mutants of Rhizobium. 719 Aug 66

H2 production from glucose by Ruminococcus albus was almost completely inhibited by 10(-5) M molybdate only when sulfide was present in the growth medium. Inhibition was accompanied by a significant increase in the production of formate. Extracts of molybdate-sulfide-grown cells did not contain hydrogenase activity. Active enzyme in extracts of uninhibited cells was not inhibited by the molybdate-sulfide-containing growth medium. The results indicate that a complex formed from molybdate and sulfide prevents the formation of active hydrogenase and electrons otherwise used to form H2 are used to reduce CO2 to formate. Growth was significantly inhibited when molybdate was increased to 10(-4) M. Reversal of growth inhibition but not inhibition of H2 production occurred between 10(-4) and 10(-3) M molybdate. H2 production by R. bromei but not by R. flavefaciens, Butyrivibrio fibrisolvens, Veillonella alcalescens, Klebsiella pneumoniae and Escherichia coli was inhibited by molybdate and sulfide.
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PMID:Molybdate and sulfide inhibit H2 and increase formate production from glucose by Ruminococcus albus. 736 26

Cell-free extracts of crotonate-grown cells of the syntrophic butyrate-oxidizing bacterium Syntrophospora bryantii contained high hydrogenase activities (8.5-75.8 mumol.min-1mg-1 protein) and relatively low formate dehydrogenase activities (0.04-0.07 mumol.min-1 mg-1 protein). The KM value and threshold value of the hydrogenase for H2 were 0.21 mM and 18 microM, respectively, whereas the KM value and threshold value of the formate dehydrogenase for formate were 0.22 mM and 10 microM, respectively. Hydrogenase, butyryl-CoA dehydrogenase and 3-OH-butyryl-CoA dehydrogenase were detected in the cytoplasmic fraction. Formate dehydrogenase and CO2 reductase were membrane-bound, likely located at the outer aspect of the cytoplasmic membrane. Results suggest that during syntrophic butyrate oxidation H2 is formed intracellularly while formate is formed at the outside of the cell.
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PMID:Localization of the enzymes involved in H2 and formate metabolism in Syntrophospora bryantii. 757 50


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