Structural properties, functional states and physiological roles of hydrogenase in photosynthetic bacteria

The membrane-bound hydrogenase from Thiocapsa roseopersicina is composed of two subunits and contains two Fe-S centres and one Ni per molecule. The enzyme resists heat and proteolytic degradation, its activity is retained under SDS-PAGE conditions. The location of the metal atoms on the subunits has been determined by proton-induced X-ray emission (PIXE). A revised hydrogenase model which concurs with the new data is suggested. The orientation of the enzyme in the photosynthetic membrane and its ability to generate membrane potential suggest that hydrogenase can play a significant role in the energetics of these bacteria. A possible link between nitrogen fixation, photosynthetic electron transport and hydrogenase is proposed.