English: A schematic representation of H2 photoproduction pathway catalyzed by a hydrogenase in cyanobacteria. As in green algae, photosynthetic electron transport delivers electrons after light-induced water-splitting at the OEC to the hydrogenases (H2-ase), leading to photophosphorylation and H2 production. In addition to hydrogenases, nitrogenases are also known to produce H2 in oxygenic cyanobacteria and in anoxygenic purple bacteria. Abbreviations: PQ, plastoquinone; Fd, ferredoxin; FNR, ferredoxin–NADP reductase; ATPase, adenosine triphosphate. The figure is modified and adapted from Shevela and Messinger (2011).