Efficiency of Hydrogen Photoproduction by Chloroplast-Bacterial Hydrogenase Systems

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Abstract
A comparative study of H2 photoproduction by chloroplasts and solubilize chlorophyll was performed in the presence of hydrogenase preparations of C.ostridium butyricum. The photoproduction of H2 by chloroplasts [pea cv. Pobeditel] in the absence of exogenous electron donors, and with irreversibly oxidized dithiothreitol and cysteine, is thought to be limited by a cyclic transport of electrons wherein methylviologen short-circuits the electron transport in photosystem I. The efficiency of H2 photoproduction by chloroplasts with ascorbate and NADPH is limited by a back reaction between light-reduced methylviologen and the oxidized electron donors. The use of a combination of electron donors (dithiothreitol and ascorbate), providing anaerobiosis without damage to chloroplasts, makes it possible to avoid consumption of reduced methylviologen for the reduction of oxidized electron donors and to exclude the short-circuiting of electron transfer. Under these conditions, photoproduction of H2 was observed to occur with a rate of 350-400 .mu.mol H2/mg chlorophyll/h. The full electron-transferring capability of photosystem I (measured by irreversible photoreduction of methyl red or O2) is used to produce H2.