H2 and CO2 Evolution by Anaerobically Adapted Chlamydomonas reinhardtii F-60

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Abstract
Using manometric and enzymic techniques, H2 and CO2 evolution in darkness and light has been studied in the green alga Chlamydomonas reinhardtii F-60. F-60 is a mutant strain characterized by an incomplete photosynthetic carbon reduction cycle but an intact electron transport chain. In the dark, starch was broken down, and H2 and CO2 was released. The uncoupler, carbonyl cyanide m-fluorophenylhydrazone with an optimum concentration of 5 to 10 micromolar, increased the rate of CO2 release and starch breakdown but depressed H2 formation. It was suggested that carbonyl cyanide m-fluorophenylhydrazone increased the rate of starch breakdown by making the chloroplast membrane permeable to H+, removing a rate-limiting step, and leading to an altered fermentative pattern. Photoevolution of H2 and CO2, but not starch breakdown, was stimulated by acetate. Maximum stimulation occurred at concentrations from 1 to 10 millimolar. Carbonyl cyanide m-fluorophenylhydrazone stimulated starch breakdown and CO2 and H2 release in the light, but not to the extent of acetate. Inasmuch as the uptake and subsequent metabolism of acetate required ATP, it was suggested that acetate, like carbonyl cyanide m-fluorophenylhydrazone, stimulated H2 photoproduction by removing ATP which limited the sequence of reactions. The contribution of photosystem II to the photoproduction of H2, as judged from the effect of 10 micromolar 3-(3,4-dichlorophenyl)-1, 1-dimethylurea, was at least 80%. CO2 photoevolution increased linearly with time, but H2 photoevolution occurred in two phases: a rapid initial phase followed by a second slower phase. The rate of H2 release increased hyperbolically with light intensity, but the rate of CO2 production tended to level off and decrease with increasing light intensity, up to 145 watts per square meter. It was proposed that a changing CO2 and H2 ratio is the result of interaction between the carbon and hydrogen metabolism and the photosynthetic electron transport chain.