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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)

Nostoc punctiforme ATCC 29133 is a nitrogen-fixing, heterocystous cyanobacterium of symbiotic origin. During nitrogen fixation, it produces molecular hydrogen (H(2)), which is recaptured by an uptake hydrogenase. Gas exchange in cultures of N. punctiforme ATCC 29133 and its hydrogenase-free mutant strain NHM5 was studied. Exchange of O(2), CO(2), N(2), and H(2) was followed simultaneously with a mass spectrometer in cultures grown under nitrogen-fixing conditions. Isotopic tracing was used to separate evolution and uptake of CO(2) and O(2). The amount of H(2) produced per molecule of N(2) fixed was found to vary with light conditions, high light giving a greater increase in H(2) production than N(2) fixation. The ratio under low light and high light was approximately 1.4 and 6.1 molecules of H(2) produced per molecule of N(2) fixed, respectively. Incubation under high light for a longer time, until the culture was depleted of CO(2), caused a decrease in the nitrogen fixation rate. At the same time, hydrogen production in the hydrogenase-deficient strain was increased from an initial rate of approximately 6 micro mol (mg of chlorophyll a)(-1) h(-1) to 9 micro mol (mg of chlorophyll a)(-1) h(-1) after about 50 min. A light-stimulated hydrogen-deuterium exchange activity stemming from the nitrogenase was observed in the two strains. The present findings are important for understanding this nitrogenase-based system, aiming at photobiological hydrogen production, as we have identified the conditions under which the energy flow through the nitrogenase can be directed towards hydrogen production rather than nitrogen fixation.
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PMID:Gas exchange in the filamentous cyanobacterium Nostoc punctiforme strain ATCC 29133 and Its hydrogenase-deficient mutant strain NHM5. 1506 6

The purple sulphur phototrophic bacterium, Thiocapsa roseopersicina BBS, contains several NiFe hydrogenases. One of these enzymes (HynSL) is membrane associated, remarkably stable and can be used for practical applications. HupSL is also located in the photosynthetic membrane, its properties are similar to other known Hup-type NiFe hydrogenases. A third hydrogenase activity was located in the soluble fraction and was analogous to the NAD-reducing hydrogenases of cyanobacteria. The hoxEFUYH genes are transcribed together. HoxE is needed for the in vivo electron flow to and from the soluble hydrogenase. Some of the accessory genes were identified using random mutagenesis, and sequencing of the T. roseopersicina genome is in progress. The HupD, HynD and HoxW gene products corresponded to the proteases processing the C-termini of the three NiFe hydrogenases respectively. HypF and HupK mutants displayed significant in vivo H(2) evolution, which could be linked to the nitrogenase activity for the DeltahypF and to the bidirectional Hox activity in the DeltahupK strain. Both HypC proteins are needed for the biosynthesis of each NiFe hydrogenase. The hydrogenase expression is regulated at the transcriptional level through distinct mechanisms. The expression of hynSL is up-regulated under anaerobic conditions with the participation of an FNR (fumarate and nitrate reduction regulator)-type protein, FnrT. Although the genes encoding a typical H(2) sensor (hupUV) and a two-component regulator (hupR and hupT) are present in T. roseopersicina, the system is cryptic in the wild-type BBS strain. The hupR gene was identified in the gene cluster downstream from hupSL. Introduction of actively expressed hupT repressed the hupSL gene expression as expected by analogy with other bacteria.
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PMID:The hydrogenases of Thiocapsa roseopersicina. 1566 65

In recent years, it has become evident that [Fe-S] proteins, such as hydrogenase, nitrogenase and aconitase, require a complex machinery to assemble and insert their associated [Fe-S] clusters. So far, three different types of [Fe-S] cluster biosynthetic systems have been identified and these have been designated nif, isc and suf. In the present work, we show that the nif-specific [Fe-S] cluster biosynthetic system from Azotobacter vinelandii, which is required for nitrogenase maturation, cannot functionally replace the isc [Fe-S] cluster system used for the maturation of other [Fe-S] proteins, such as aconitase. The results indicate that, in certain cases, [Fe-S] cluster biosynthetic machineries have evolved to perform only specialized functions.
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PMID:NifU and NifS are required for the maturation of nitrogenase and cannot replace the function of isc-gene products in Azotobacter vinelandii. 1566 74

A limited number of strains belonging to several genera of Rhizobiaceae are capable of expressing a hydrogenase system that allows partial or full recycling of hydrogen evolved by nitrogenase, thus increasing the energy efficiency of the nitrogen fixation process. This review is focused on the genetics and biotechnology of the hydrogenase system from Rhizobium leguminosarum bv. viciae, a frequent inhabitant of European soils capable of establishing symbiotic association with peas, lentils, vetches and other legumes.
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PMID:Genetics and biotechnology of the H(2)-uptake [NiFe] hydrogenase from Rhizobium leguminosarum bv. viciae, a legume endosymbiotic bacterium. 1566 75

The electrochemical hydrogen evolution reaction is catalyzed most effectively by the Pt group metals. As H2 is considered as a future energy carrier, the need for these catalysts will increase and alternatives to the scarce and expensive Pt group catalysts will be needed. We analyze the ability of different metal surfaces and of the enzymes nitrogenase and hydrogenase to catalyze the hydrogen evolution reaction and find a necessary criterion for high catalytic activity. The necessary criterion is that the binding free energy of atomic hydrogen to the catalyst is close to zero. The criterion enables us to search for new catalysts, and inspired by the nitrogenase active site, we find that MoS2 nanoparticles supported on graphite are a promising catalyst. They catalyze electrochemical hydrogen evolution at a moderate overpotential of 0.1-0.2 V.
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PMID:Biomimetic hydrogen evolution: MoS2 nanoparticles as catalyst for hydrogen evolution. 1582 54

The principles and recent progress in the research and development of photobiological hydrogen production are reviewed. Cyanobacteria produce hydrogen gas using nitrogenase and/or hydrogenase. Hydrogen production mediated by native hydrogenases in cyanobacteria occurs under in the dark under anaerobic conditions by degradation of intracellular glycogen. In vitro and in vivo coupling of the cyanobacterial photosynthetic system with a clostridial hydrogenase via cyanobacterial ferredoxin was demonstrated in the presence of light. Genetic transformation of Synechococcus PCC7942 with the hydrogenase gene from Clostridium pasteurianum was successful; the active enzyme was expressed in PCC7942. The strong hydrogen producers among photosynthetic bacteria were isolated and characterized. Coculture of Rhodobacter and Clostriudium was applied for hydrogen production from glucose. A mutant strain of Rhodobacter sphaeroides RV whose light-harvesting proteins were altered was obtained by UV irradiation. Hydrogen productivity by the mutant was improved when irradiated with monochromatic light of some wavelengths. The development of photobioreactors for hydrogen production is also reviewed.
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PMID:Photobiological hydrogen production. 1623 64

Bradyrhizobium sp. (Lupinus) and Bradyrhizobium sp. (Vigna) mutants in which hydrogenase (hup) activity was affected were constructed and analyzed. Vigna unguiculata plants inoculated with the Bradyrhizobium sp. (Vigna) hup mutant showed reduced nitrogenase activity and also a significant decrease in nitrogen content, suggesting a relevant contribution of hydrogenase activity to plant yield.
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PMID:Symbiotic hydrogenase activity in Bradyrhizobium sp. (Vigna) increases nitrogen content in Vigna unguiculata plants. 1626 97

Analysis of levels of hydrogenase processing and activity in Rhizobium leguminosarum biovar viciae bacteroids from pea (Pisum sativum) plants showed that the oxidation of nitrogenase-evolved hydrogen is limited by the availability of nickel in agricultural soils. This limitation was overcome by using an inoculant strain engineered for higher hydrogenase expression.
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PMID:Rhizobium leguminosarum biovar viciae symbiotic hydrogenase activity and processing are limited by the level of nickel in agricultural soils. 1626 13

A series of Rhizobium meliloti and Rhizobium trifolii strains were used as inocula for alfalfa and clover, respectively, grown under bacteriologically controlled conditions. Replicate samples of nodules formed by each strain were assayed for rates of H(2) evolution in air, rates of H(2) evolution under Ar and O(2), and rates of C(2)H(2) reduction. Nodules formed by all strains of R. meliloti and R. trifolii on their respective hosts lost at least 17% of the electron flow through nitrogenase as evolved H(2). The mean loss from alfalfa nodules formed by 19 R. meliloti strains was 25%, and the mean loss from clover nodules formed by seven R. trifolii strains was 35%. R. meliloti and R. trifolii strains also were cultured under conditions that were previously established for derepression of hydrogenase synthesis. Only strains 102F65 and 102F51 of R. meliloti showed measurable activity under free-living conditions. Bacteroids from nodules formed by the two strains showing hydrogenase activity under free-living conditions also oxidized H(2) at low rates. The specific activity of hydrogenase in bacteroids formed by either strain 102F65 or strain 102F51 of R. meliloti was less than 0.1% of the specific activity of the hydrogenase system in bacteroids formed by H(2) uptake-positive Rhizobium japonicum USDA 110, which has been investigated previously. R. meliloti and R. trifolii strains tested possessed insufficient hydrogenase to recycle a substantial proportion of the H(2) evolved from the nitrogenase reaction in nodules of their hosts. Additional research is needed, therefore, to develop strains of R. meliloti and R. trifolii that possess an adequate H(2)-recycling system.
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PMID:Hydrogen Evolution from Alfalfa and Clover Nodules and Hydrogen Uptake by Free-Living Rhizobium meliloti. 1634 61

The ability to recycle H(2) evolved by nitrogenase is thought to be of importance in increasing the efficiency of N(2) fixation and to be a factor in increasing plant yield in symbiotic systems. To determine whether this ability is a significant factor in the Rhizobium leguminosarum-Pisum sativum L. system, plants were inoculated with R. leguminosarum isolates which differed in their ability to oxidize H(2) and in their relative efficiency of N(2) fixation. These plants were grown at three levels of irradiance and harvested after 3, 4, and 5 weeks of growth for determination of C(2)H(2) reduction, H(2) evolution and uptake, plant dry weight, and N content. Plants inoculated with uptake hydrogenase-positive (Hup) isolates did not exhibit higher dry weight or N content than those inoculated with Hup isolates under any of the growth conditions studied. The efficiency of the nitrogenase system of Hup isolates increased at a low irradiance, a factor which may allow them to compete successfully with Hup isolates. In some HupR. leguminosarum isolates, H(2) oxidation is coupled to ATP formation, whereas in others, it is not. There were no differences in plant dry weight and N content in plants inoculated with the two types and grown for 5 weeks at three irradiance levels. The addition of H(2) to Hup nodules whose supply of photosynthate had been removed by stem excision did not increase C(2)H(2) reduction in either coupled or uncoupled types.
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PMID:Hydrogen Recycling by Rhizobium leguminosarum Isolates and Growth and Nitrogen Contents of Pea Plants (Pisum sativum L.). 1634 48


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