Efficiency of Hydrogen Photoproduction by Chloroplast-Bacterial Hydrogenase Systems

AUTOR(ES)

Krasnovsky, A. A.

RESUMO

A comparative study of H2 photoproduction by chloroplasts and solubilized chlorophyll was performed in the presence of hydrogenase preparations of Clostridium butyricum. The photoproduction of H2 by chloroplasts 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 to 400 micromoles H2 per milligram chlorophyll per hour. In this case, the full electron-transferring capability of photosystem I (measured by irreversible photoreduction of methyl red or O2) is used to produce H2.

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