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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 addition of exogenous cyclic guanosine 3',5'-monophosphate (cGMP) at a concentration of 0.1 mM to a free-living culture of Rhizobium japonicum 3I1b110 was found to completely inhibit the expression of nitrogenase activity and markedly inhibit the expression of hydrogenase and nitrate reductase activities. The effect was specific for cGMP. Experiments on the in vivo incorporation of radioactive methionine and subsequent analysis of the labeled proteins on polyacrylamide gels showed that the biosynthesis of nitrogenase polypeptides was inhibited. It appears that the time of addition of cGMP is important since the effect was only seen during the early stages of nif gene expression. The intracellular level of cGMP was found to respond to physiological changes in the cell, and there was a fall in cGMP concentrations when nitrogenase was induced. Microaerophilic-aerobic shift experiments showed that intracellular levels increased from 0.25 pmol/mg of cell protein under microaerophilic conditions to 2.6 pmol/mg of cell protein under aerobic conditions, suggesting that the cellular pool size of cGMP may be under redox control.
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PMID:Effect of cyclic guanosine 3',5'-monophosphate on nitrogen fixation in Rhizobium japonicum. 3 37

This manuscript reviews the literature on hydrogen metabolism in blue-green algae and reports some new data from this laboratory. H2-formation by intact cells is found to be catalyzed exclusively by nitrogenase. Its rate appears to be variable from strain to strain used byt is--in our hands--very small. Therefore, blue-green algae are presumably of limited value in projects of solar energy conversion to form molecular hydrogen. These organisms are also able to consume the gas in a reaction catalysed by hydrogenase. Hydrogen is mainly consumed in an oxygen dependent reaction, as in aerobic nitrogen fixing bacteria. It can also serve as an electron donor for nitrogen fixation under certain physiological conditions. In experiments with a cell-free preparation, hydrogenase is found to be membrane-bound. The enzyme is characterized with respect to its specifity towards electron donors and acceptors.
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PMID:Hydrogen metabolism in blue-green algae. 9 76

A method was devised that allows measurement in vivo of hydrogenase-catalysed H2 evolution from the cyanobacterium Anabaena cylindrica, independent of nitrogenase activity, which is also present. Addition of low concentrations of reduced Methyl Viologen (1-10mM) to intact heterocystous filaments of the organism resulted in H2 evolution, but produced conditions giving total inhibition of nitrogenase (acetylene-reducing and H2-evolving) activity. That the H2 formed under these conditions was not contributed to by nitrogenase was also supported by the observation that its rate of formation was similar in the dark or with Ar replaced by N2 in the gas phase, and also in view of the pattern of H2 evolution at very low Methyl Viologen concentrations. Conclusive evidence that the H2 formed in the presence of Methyl Viologen was solely hydrogenase-mediated was its evolution even from nitrogenase-free (non-heterocystous) cultures; by contrast 'uptake' hydrogenase activity in such cultures was greatly decreased. The hydrogenase activity was inhibited by CO and little affected by acetylene. Finally the hydrogenase activity was shown to be relatively constant at different stages during the batch growth of the organism, as opposed to nitrogenase activity, which varied.
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PMID:Measurement in vivo of hydrogenase-catalysed hydrogen evolution in the presence of nitrogenase enzyme in cyanobacteria. 10 42

The thylakoids of vegetative cells of the filamentous cyanobacterium, Anabaena cylindrica, are capable of oxygen-evolving photosynthesis and contain both Photosystems I and II (PSI and PSII). The heterocysts, cells specialized for nitrogen fixation, do not produce oxygen and lack Photosystem II activity, the major accessory pigments, and perhaps the chlorophyll a associated with PSII. Freeze-fracture replicas of vegetative cells and of heterocysts reveal differences in the structure of the thylakoids. A histogram of particle sizes on the exoplasmic fracture face (E-face, EF) of vegetative cell thylakoids has two major peaks, at 75 and 100 A. The corresponding histogram for heterocyst thylakoids lacks the 100 A size class, but has a very large peak at about 55 A with a shoulder at 75 A. Histograms of protoplasmic fracture face (P-face, PF) particle diameters show single broad peaks, the mean diameter being 71 A for vegetative cells and 64 A for heterocysts. The thylakoids of both cell types have about 5600 particles/micrometers2 on the P-face. On the E-face, the density drops from 939 particles/micrometers2 on vegetative cell thylakoids to 715 particles/micrometers2 on heterocyst thylakoids. The data suggest that the 100 A E-face particle of vegetative cell thylakoids is a PSII complex. The 55 A EF particle of heterocysts may be part of the nitrogenase complex or a remnant of the PSII complex. The role of the 75 A EF particle is unknown. Other functions localized on cyanobacterial thylakoids, such as respiration and hydrogenase activity, must be considered when interpreting the structure of these complex thylakoids.
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PMID:Changes in thylakoid structure associated with the differentiation of heterocysts in the cyanobacterium, Anabaena cylindrica. 11 Mar 42

The cells of Rhodospirillum rubrum and Thiocapsa roseopersicina grown in media containing glutamate and arginine, respectively, as well as under conditions of nitrogen fixation evolve H2 in the light. If the cultures were grown in media with NH4+, NO3-, urea, glutamine or asparagine, hydrogen photoevolution by the cells and acetylene reduction started after the lag-phase and proceeded at a low rate. Extracts of such cells did not display the activity of nitrogenase which could be assayed by the ATP-dependent evolution of H2 from dithionite. The data obtained confirm the fact that hydrogen photoevolution by purple bacteria involves nitrogenase whose synthesis is regulated (according to the action of glutamine) with the participation of glutamine synthetase. NH4+, glutamine and asparagine inhibit also hydrogen photoproduction by purple bacteria and acetylene photoreduction. However, they have no effect on hydrogen evolution in the dark by the cells of R. rubrum and T. roseopersicina in the presence of formiate or pyruvate, respectively, whereas carbon monoxide inhibits hydrogen production. Therefore, hydrogen production by purple bacteria in the dark must be catalyzed by hydrogenase.
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PMID:[Effect of nitrogen-containing compounds on hydrogen light emission and nitrogen fixation by purple bacteria]. 11 58

Hydrogenase from C. pasteurianum is an iron-sulfur protein containing at least two tetrameric iron-sulfur centers. Information on the structure of the remaining iron atoms must await future investigation. Although the EPR spectra of dithionite-reduced hydrogenase and eight-iron Fd showed some similarity, the CD spectra clearly indicated a difference. The tetrameric iron-sulfur centers of hydrogenase were shown to undergo redox changes when hydrogenase was oxidized or reduced. However, no evidence is now available to support a role for the tetrameric Fe-S centers, responsible for the EPR spectrum A, as the primary site for H2 binding and activation. Because we have found that the [Fe4S4(SR)4]-containing ferredoxins do not have hydrogenase activity, it is conceivable that the additional iron atoms and/or certain amino acid residues of hydrogenase also contribute to the unique catalytic properties of this enzyme. Chemical synthesis of Fe-S clusters with different peptide environments and with hydrogenase function would lead to the identification of these functional groups. X-ray diffraction studies on hydrogenase will certainly complement the other approaches. Knowledge of the structure of the active site of hydrogenase will certainly accelerate research into: (1) the synthesis of a stable catalyst to replace hydrogenase in systems designed to produce H2 by coupling this catalyst to a photoreducing system; and (2) the elucidation of the active sites of more complicated iron-sulfur enzymes such as nitrogenase.
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PMID:The iron-sulfur centers and the function of hydrogenase from Clostridium pasteurianum. 18 83

Purple bacteria Rhodospirillum rubrum and Thiocapsa roseopersicina form two enzymes, hydrogenase and nitrogenase, which participate in hydrogen metabolism. H2 photoproduction in these bacteria is associated mainly or completely with the action of nitrogenase. The soluble and membrane-bound hydrogenases of T. roseopersicina have similar physicochemical properties (mol. weight, subunit composition, N-terminal amino acids, Fe2+ and S2- content, pl. Eo'). In comparison with other hydrogenases the enzyme from R. rubrum and T. roseopersicina evolve H2 with high rate from reduced cytochrome c3, but not from ferredoxins. H2 production and N2 fixation take place in the presence of NAD(P)H. NADP-reductase, ferredoxin and cytochrome c3 participate in this reaction. Possible relationships between hydrogenase-nitrogenase in the metabolism of molecular hydrogen are discussed.
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PMID:Relationships in hydrogen metabolism between hydrogenase and nitrogenase in phototrophic bacteria. 20 59

An investigation was made of certain factors involved in the formation of hydrogen gas, both in an anaerobic environment (argon) and in air, by the blue-green alga Anabaena cylindrica. The alga had not been previously adapted under hydrogen gas and hence the hydrogen evolution occurred entirely within the nitrogen-fixing heterocyst cells; organisms grown in a fixed nitrogen source, and which were therefore devoid of heterocysts, did not produce hydrogen under these conditions. Use of the inhibitor dichlorophenyl-dimethyl urea showed that hydrogen formation was directly dependent on photosystem I and only indirectly dependent on photosystem II, consistent with heterocysts being the site of hydrogen formation. The uncouplers carbonyl cyanide chlorophenyl hydrazone and dinitrophenol almost completely inhibited hydrogen formation, indicating that the process occurs almost entirely via the adenosine 5'-triphosphate-dependent nitrogenase. Salicylaldoxime also inhibited hydrogen formation, again illustrating the necessity of photophosphorylation. Whereas hydrogen formation could usually only be observed in anaerobic, dinitrogen-free environments, incubation in the presence of the dinitrogen-fixing inhibitor carbon monoxide plus the hydrogenase inhibitor acetylene resulted in significant formation of hydrogen even in air. Hydrogen formation was studied in batch cultures as a function of age of the cultures and also as a function of culture concentration, in both cases the cultures being harvested in logarithmic growth. Hydrogen evolution (and acetylene-reducing activity) exhibited a distinct maximum with respect to the age of the cultures. Finally, the levels of the protective enzyme, superoxide dismutase, were measured in heterocyst and vegetative cell fractions of the organism; the level was twice as high in heterocyst cells (2.3 units/mg of protein) as in vegetative cells (1.1 units/mg of protein). A simple procedure for isolating heterocyst cells is described.
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PMID:Anaerobic and aerobic hydrogen gas formation by the blue-green alga Anabaena cylindrica. 41 67

Hydrogen evolved by nitrogenase may be recycled by a hydrogenase present in some legume nodules. Anoka and Portage cultivars of soybeans were inoculated with each of 8 and 24 strains, respectively, of Rhizobium japonicum and surveyed for H2 evolution and C2H2 reduction rates nodule weight, and plant dry weight. Six of the strains (3Ilb 110, USDA 122, USDA 136, 3Ilb 6, 3Ilb 142, and 3Ilb 143) which exhibited no H2 evolution in air were shown to take up H2. The relative efficiencies of nitrogenase energy utilization based on C2H2 reduction rates of nodules relative efficiences of nitrogenase energy utilization based on C2H2 reduction rates of nodules ranged from 0.96 to 1.0 for the six strains. Nodules formed by strain WA 5099-1-1 evolved small amounts of H2 in air and had a relative efficiency of 0.92. Nodules formed by the remaining 25 strains had relative efficiencies ranging from 0.41 to 0.80. A H2-evolving (3Ilb 123) and non-H2-evolving (3Ilb 143) strain were tested on seven soybean cultivars to determine the effect on the expression of hydrogenase. Nodules formed by strain 3Ilb 143 exhibited an efficiency of 1.0 on the following cultivars: Amsoy 71, Anoka, Bonus, Clark 63, Kent, Peking, and Portage. Relative efficiencies from 0.63 to 0.77 were determined for the five cultivars nodulated by strain 3Ilb 123. From the experiments with these cultivars, the capacity to recycle H2 produced from the nitrogenase system appears to be determined by the R. japonicum strain.
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PMID:Hydrogen evolution and uptake by nodules of soybeans inoculated with different strains of Rhizobium japonicum. 56 72

H2 will support nitrogenase activity (C2H2 reduction) in Azotobacter chroococcum with or without added carbon substrate. Results show that H2 is metabolised to transfer electrons to nitrogenase and to the respiratory chain to produce ATP. H2-supported nitrogenase activity is most significant at low carbon substrate concentrations, but also occurs at saturating concentration. Continuous cultures of N2-fixing A. chroococcum evolved H2 from nitrogenase under O2-N2- and C-limited conditions. This H2 represented a significant proportion of nitrogenase activity. Hydrogenase activity was consistently high under C-limited conditions, but low or undetectable under O2- and N2-limitations. Pre-treatment with 40 per cent C2H2 inhibited hydrogenase activity in C-limited cultures, and H2 evolution increased under air and under Ar:O2 (4:1) mixtures. We deduce that hydrogenase : I, recycles H2 produced by nitrogenase to provide electrons and energy for N2 reduction: II, supports respiratory protection for nitrogenase under C-limited conditions, and III, does not act to prevent any inhibition of N2 reduction by H2 produced by nitrogenase. A scheme for the H2 cycle in N2-fixing A. chroococcum is proposed.
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PMID:The hydrogen cycle in nitrogen-fixing Azotobacter chroococcum. 66 78


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