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 variation with redox potential of nitrogenase activity and the ratio of ATP hydrolyzed per two electrons transferred were measured using two systems: the dithionite/bisulfite couple at pH 7.4; and H2, hydrogenase, and ferredoxin at pH 8.5. In both cases, the variation in nitrogenase activity with redox potential followed a theoretical Nernst plot for a two-electron process with an apparent midpoint potential of about -470 mV. The ratio ATP/2e- was about 4 under highly reducing conditions. However, above the apparent midpoint potential, the ratio ATP/2e- increased drastically, reaching values as high as 20. These data imply that a low redox potential must be maintained for efficient nitrogen fixation in vitro and in vivo.
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PMID:Nitrogenase reduction by electron carriers: influence of redox potential on activity and the ATP/2e- ratio. 657 45

A minimally defined medium was developed for the cultivation of the acetogen Clostridium thermoaceticum. The medium contained glucose as the carbon and energy source, ammonium sulfate as the nitrogen source, nicotinic acid as the sole essential vitamin, reductant, a phosphate-bicarbonate buffer, mineral salts and chelator, and a CO2 gas phase. Adaptation of C. thermoaceticum from undefined medium containing yeast extract and tryptone to the minimally defined medium required sequential passage on defined medium supplemented with amino acids and vitamins. Growth and cell yields were reduced on the minimal medium, but the activities of carbon monoxide dehydrogenase, hydrogenase, and formate dehydrogenase were comparable between undefined and minimal media.
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PMID:Development of a minimally defined medium for the acetogen Clostridium thermoaceticum. 674 75

Recently reported research from this laboratory has demonstrated the autotrophic growth of certain hydrogen-uptake-positive strains of Rhizobium japonicum and defined minimal conditions for such growth. Ribulose 1,5-bisphosphate carboxylase has been detected in autotrophically growing cells, but at low specific activity. Moreover, growth rates were low, and growth ceased at low cell densities. We report here improved autotrophic growth rates of R. japonicum SR through the use of a modified mineral salts/vitamins medium and a programmed increase in oxygen tension as autotrophic growth proceeds. Under these conditions, ribulose, 1,5-biphosphate carboxylase activity increased greater than 10-fold and crude-extract-uptake-hydrogenase activities were from 20 to 47 times those heretofore reported for free-living R. japonicum. It is likely that previous assays for these enzymes were done on preparations of cells in which their synthesis had been partially repressed. The contribution of CO2 fixation to organic carbon accumulation in autotrophic cells was assessed as sufficient to support observed growth. Enzymological determination of the product of carbon fixation has established a stoichiometric ratio of 1.9 mol of 3-phosphoglycerate per mol of CO2 fixed and unequivocally assigns the role of carbon fixation catalysis to ribulose 1,5-bisphosphate carboxylase. Ammonium served best as a nitrogen source, nitrate was less effective, and gaseous nitrogen would not support autotrophic growth. Ecological, evolutionary, and practical considerations of autotrophy in the rhizobia are briefly discussed in the light of our findings.
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PMID:Chemoautotrophic growth of hydrogen-uptake-positive strains of Rhizobium japonicum. 676 87

An examination of conditions for the growth of Desulfovibrio desulfuricans, with the aim of optimizing hydrogenase production, is reported. An ammonium sulfate-lactate-yeast extract medium gave 5 to 10 times as much hydrogenase activity as a peptone-yeast extract medium. It made little if any difference whether the gas used for sparging was nitrogen, hydrogen, or a mixture thereof but increasing the rate of sparging and agitation did result in a slight decrease in activity. Control of pH during culture development was of little benefit to hydrogenase production. At least two hydrogenases were present in D. desulfuricans: one periplasmic, the other membrane bound.
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PMID:Factors affecting the production of hydrogenase by Desulfovibrio desulfuricans. 700 64

The chelating agents EDTA, o-phenanthroline, nitrilotriacetic acid (NTA), ethylenediamine-bis(o-hydroxyphenylacetic acid) (EDDA) or dimethylglyoxime prevented the expression of hydrogenase activity in batch cultures of nitrogen-fixing Azotobacter chroococcum, but did not inhibit preformed enzyme. The inhibition was reversed either by adding a mixture of trace elements (Cu2+, Mn2+, Zn2+, Co2+) or Ni2+ or, to a lesser degree, Co2+ alone. Ni2+ or Ni2+ + Fe2+ also enhanced the rate of hydrogenase derepression in A. chroococcum in the absence of any added chelator, if the medium was first extracted with 8-hydroxyquinoline. A. chroococcum accumulated 63Ni2+ by an energy-independent mechanism. Both, Ni2+ uptake and hydrogenase synthesis were equally inhibited by either NTA, EDTA, EDDA or dimethylglyoxime. The evidence suggests a role for Ni2+ in hydrogenase synthesis.
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PMID:Effect of chelating agents on hydrogenase in Azotobacter chroococcum. Evidence that nickel is required for hydrogenase synthesis. 705 66

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

A major simplification of the methyl coenzyme M methylreductase system of Methanobacterium has been effected. The 500,000-dalton hydrogenase complex has been replaced by an NADPH-coenzyme F420 oxidoreductase. By use of this electron-generating reaction, the methylreductase was found to be localized in component C, an acidic protein fraction. In the presence of the oxidoreductase and the methylreductase, formation of methane under a nitrogen atmosphere was dependent upon the addition of NADPH, coenzyme F420, component B (a new cofactor of unknown structure), ATP, Mg2+, and methyl coenzyme M.
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PMID:Role of component C in the methylreductase system of Methanobacterium. 741 Mar 69

Pea (Pisum sativum L.) bacteroids produced by Rhizobium leguminosarum bv. viciae UPM791 synthesize a membrane-bound (NiFe) hydrogenase which oxidizes H2 arising from the nitrogen fixation process in root nodules. Synthesis of the active enzyme requires the products of the structural genes hupSL and an array of accessory proteins from at least 15 additional genes, including the gene cluster hypABFCDE, likely involved in nickel metabolism. Unlike the hupSL genes, which are expressed only in symbiosis, the hypBFCDE operon was also activated in vegetative cells in response to low pO2 in the culture medium. In microaerobic cells and in bacteroids, transcription of the hypBFCDE operon occurred from a promoter, P5b, with a transcription initiation site located 190 bp upstream of the ATG start codon of hypB, within the coding sequence of hypA. Transcription start site 5b was preceded by an Fnr box (anaerobox), 5'-TTGAgccatgTCAA-3', centered at position -39.5. Expression of the P5b promoter in the heterologous Rhizobium meliloti bacterial host was dependent on the presence of an active fixK gene. A 2.6-kb EcoRI fragment was isolated from an R. leguminosarum bv. viciae UPM791 gene bank by complementing an R. meliloti FixK- mutant. Sequencing of this DNA fragment identified an fnrN gene, and cassette insertion mutagenesis demonstrated that R. leguminosarum bv. viciae fnrN is able to replace the R. meliloti fixK gene for activation of both the R. leguminosarum bv. viciae hypBFCDE operon and the R. meliloti fix genes. However, bacteroids from a genomic FnrN- mutant of R. leguminosarum bv. viciae exhibited wild-type levels of hydrogenase activity. Microaerobic expression of P(5b) was reduced to ca. 50% of the wild-type level in the FnrN(-) mutant. These results indicate that hyp gene expression escapes mutagenesis of the fnrN gene and suggest the existence of a second fnr-like gene in R. leguminosarum by. viciae. Southern blot analysis with an fnrN internal probe revealed the presence of a second genomic region with homology to fnrN.
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PMID:The hypBFCDE operon from Rhizobium leguminosarum biovar viciae is expressed from an Fnr-type promoter that escapes mutagenesis of the fnrN gene. 755 56

In Rhodobacter capsulatus, the hupL gene encoding the large subunit of the uptake-hydrogenase (Hup) enzyme complex was mutated by insertion of an interposon. The mutant neither synthesized an active hydrogenase nor grew photoautotrophically. Under conditions of nitrogen (N) limitation, photoheterotrophic cultures of the wild type and the mutant evolved H2 by activity of the nitrogenase enzyme complex. When grown with glutamate as an N source and either D,L-malate or L-lactate as carbon sources, the efficiency of H2 production by the HupL mutant was higher than 90%, whereas wild-type cultures exhibited efficiencies of 54% (with D,L-malate) and 64% (with L-lactate), respectively. With NH4+ as the N source, efficiencies of H2 production were 70% (mutant) and 52% (wild type).
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PMID:Optimizing photoheterotrophic H2 production by Rhodobacter capsulatus upon interposon mutagenesis in the hupL gene. 776 18

Programmed DNA rearrangements that occur during cellular differentiation are uncommon and have been described in only two prokaryotic organisms. Here, we identify the developmentally regulated rearrangement of a hydrogenase gene in heterocysts of the cyanobacterium Anabaena sp. strain PCC 7120. Heterocysts are terminally differentiated cells specialized for nitrogen fixation. Late during heterocyst differentiation, a 10.5-kb DNA element is excised from within the hupL gene by site-specific recombination between 16-bp direct repeats that flank the element. The predicted HupL polypeptide is homologous to the large subunit of [NiFe] uptake hydrogenases. hupL is expressed similarly to the nitrogen-fixation genes; hupL message was detected only during the late stages of heterocyst development. An open reading frame, named xisC, identified near one end of the hupL DNA element is presumed to encode the element's site-specific recombinase. The predicted XisC polypeptide is homologous with the Anabaena sp. strain PCC 7120 site-specific recombinase XisA. Neither XisC nor XisA shows sequence similarity to other proteins, suggesting that they represent a different class of site-specific recombinase.
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PMID:Programmed DNA rearrangement of a cyanobacterial hupL gene in heterocysts. 784 53


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