The electron transfer pathway upon H2 oxidation by the NiFe bidirectional hydrogenase of Synechocystis sp. PCC 6803 in the light shares components with the photosynthetic electron transfer chain in thylakoid membranes

Abstract In anaerobic conditions the NiFe hydrogenase in the cyanobacterium Synechocystis sp. PCC 6803 catalyzes transient H 2 production upon a darkness-to-light transition, followed by a rapid H 2 uptake. We measured H 2 uptake in Synechocystis mutants lacking photosystem I, photosystem II or terminal oxidases and in the wild-type strain with and without active cytochrome b 6 f . Rapid light-induced H 2 uptake was dependent on cytochrome b 6 f and the presence of photosystem I. We propose light-dependent electron transport from H 2 to plastoquinone, probably via NAD(P)H dehydrogenase, and on to cytochrome b 6 f and photosystem I. In darkness H 2 uptake is ∼10-fold slower than in the light and is independent of thylakoid redox components. The plastoquinone redox state may be key in determining the ultimate H 2 redox partner. H 2 uptake and production in darkness likely use the same redox partners. NADH and NADPH, but not reduced ferredoxin, were confirmed as hydrogenase redox donors in vitro .