The significance of hydrogenase activity for the energy metabolism of green algae: anaerobiosis favours ATP synthesis in cells of Chlorella with active hydrogenase
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In cells of the green alga Chlorella fusca, which contain active hydrogenase(s), the concentration of ATP, NADH and NADPH were measured during a 5 h period of anaerobiosis in the dark and upon subsequent illumination with high light intensities (770 W/m2), conditions which favour optimal hydrogen photoproduction.
ATP concentrations were also determined in cells of Chlorella fusca, whose hydrogenase was inactivated prior to illumination, and in cells of Chlorella vulgaris which do not contain hydrogenase. In the dark, the ATP concentration increased slightly during anaerobiosis in cells with active hydrogenase. This increase in ATP concentration was accompanied by an increase of NADH and a decrease of NADPH content.
Upon illumination, the ATP content increased in cells with an active hydrogenase, whereas the NADH content decreased. The rate of phosphorylation was twice that observed in cells without active hydrogenase.
This ATP synthesis in the light was not inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) (10 μmol/l) nor by carbonylcyanide-3-chlorophenyl-hydrazone (CCCP) (1 μmol/l) but was diminished by 500 μmol/l dibromothymoquinone (DBMIB) and 6 μmol/l carbonylcyanide-3-chlorophenyl-hydrazone (CCCP).
It was concluded that an active hydrogenase can support ATP production under anaerobic conditions in the dark as well as in the light. NADH might serve in vivo as electron donor for a fermentative production of hydrogen in the light.
Possible mechanisms underlying ATP production under anaerobiosis and hydrogen productive conditions are discussed.
Key wordsGreen algae Chlorella fusca Chlorella vulgaris Hydrogenase Anaerobiosis Energy metabolism ATP NADH NADPH
II, photosystem I, II respectively
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