LIMITING REACTIONS IN HYDROGEN PHOTOPRODUCTION BY CHLOROPLASTS AND HYDROGENASE

Abstract— Hydrogen was photoproduced from water in a system containing isolated chloroplasts, hy-drogenase, a coupling electron carrier (ferredoxin or methyl viologen), and an oxygen scavenger. The rate and extent of hydrogen production anaerobically was much less than the rate of aerobic electron-carrier reduction by chloroplasts and was not limited by hydrogenase. The limiting reaction in the coupled system was the extent of reduction of methyl viologen anaerobically rather than its oxidation by oxygen produced during the course of the reaction. Inhibition of photosystem II by 3-(3,4dichlorophenyl)-1,1-dimethylurea and addition of a photosystem 1 electron donor did not lead to photoproduction of hydrogen or photoreduction of methyl viologen. Extensive photosystem I hydrogen evolution was obtained when thiols were also present. Platinum asbestos or palladium asbestos replaced hydrogenase in a system coupled to chloroplasts.