The turnover times and pool sizes of photosynthetic hydrogen production by green algae

Abstract

An investigation of the turnover times of photobiological production of hydrogen gas by green algae indicate that the photoreactions associated with molecular hydrogen production have promising properties for solar energy conversion and storage. Our results indicate that (a) the intrinsic kinetic rate capability of the hydrogen photoapparatus in green algae can keep pace with the incidence rate of light quanta, even in full sunlight; (b) the photogenerated electrons for hydrogen production probably lie in the mainstream of the electron transport chain of photosynthesis. These results have been obtained by performing the first measurements on the turnover times and pool sizes of photosynthetic hydrogen production. For the three species of green algae studied, the turnover times range from 0.1 to 3 ms. The turnover time for photosynthetic hydrogen production is, therefore, comparable to that for oxygen production. Rapid multiple flash experiments have been performed which indicate that the immediate source of reductant for photosynthetic hydrogen production is derived from a pool of 5–20 equivalents, depending on the alga. This pool is probably the plastoquinone pool linking the two photosystems of photosynthesis.