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)

1. It has been shown that redox equilibria can be formed between dithionite ion (plus SO-2) and (bi)sulphite, and the low-potential electron carriers flavodoxin and methyl viologen. The equilibria were established either by treating the oxidized electron carriers with dithionite, or by treating flavodoxin hydroquinone or methyl viologen semiquinone with (bi)sulphite. Similar redox equilibria were established between dithionite/(bi)sulphite and hydrogen using catalytic amounts of hydrogenase in the presence of a low-potential electron carrier. The effects of pH and temperature on the equilibria were determined. 2. The equilibria were analyzed to determine the redox potential of the dithionite/(bi)sulphite system. In accordance with the results of earlier kinetic studies, it was assumed that the reductant in dithionite solutions is the dissociation product SO-2. The calculated midpoint redox potential E' for the couple SO-2/HSO-3 at pH 7 and 25 degrees C was -0.66 V. The reductant is present largely as the dimer at concentrations of dithionite above about 10nM. Consequently, the midpoint potential, Em, of dithionite solutions becomes less negative as the concentration of dithionite is increased (deltaEm/deltalog S2O2-4 = 29 mV). The theoretical potential of a solution of 1 M S2O2-4 and 2 M (bi)sulphite at pH 7 was calculated to be -0.386V. This value is 59 mV more negative than that determined in 1911 by potentiometry, but considerably more positive than other values in the literature. The effects of pH on the equilibria showed that E' is controlled by the pK of (bi)sulphite at 6.9; the slope deltaE'/deltapH was -59 mV below the pK and -118 mV above the pK. The effects of temperature on the equilibria suggested that Em for dithionite changed by -1.6 mV/degrees C for a rise in temperature between 2 degrees C and 40 degrees C. If sodium dithionite is contaminated with small amounts of (bi)sulphite, its addition in large excess to a low potential electron carrier can cause oxidation of the carrier.
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PMID:The redox potential of dithionite and SO-2 from equilibrium reactions with flavodoxins, methyl viologen and hydrogen plus hydrogenase. 64 33

The reversible hydrogenase from Anabaena 7120 appeared when O(2) was continuously removed from a growing culture. Activity increased further when cells were incubated under argon in the dark or in the light plus 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Hydrogenase existed in an inactive state during periods of O(2) evolution. It could be reductively activated by exposure to reduced methyl viologen or by dark, anaerobic incubation. Hydrogenase-containing cells evolved H(2) slowly during dark anaerobic incubations, and the rate of H(2) evolution was increased by illumination with low intensity light. Light enhancement of H(2) evolution was of short duration and was eliminated by the ferredoxin antagonist disalicylidene diaminopropane. Physiological acceptors that supported H(2) uptake included NO(3) (-), NO(2) (-), and HSO(3) (-), and light had a slight influence on the rate of H(2) uptake with these acceptors. Low levels of O(2) supported H(2) uptake, but higher concentrations of O(2) inactivated the hydrogenase. Hydrogen uptake with HCO(3) (-) as acceptor was the most rapid reaction measured, and it was strictly light-dependent. It occurred only at low light intensities, and higher light intensities restored normal O(2)-evolving photosynthesis. It is suggested that hydrogenase is present to capture exogenous H(2) as a source of reducing equivalents during growth in anaerobic environments.
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PMID:Physiological reactions of the reversible hydrogenase from anabaena 7120. 1666 86