Evidence for Nickel in the Soluble Hydrogenase from the Unicellular Green Alga Scenedesmus obliquus

Cultures of the green alga Scenedesmus obliquus were grown in the presence of either the chelating reagent EDTA or NiCl in various concentrations and assayed for hydrogenase catalyzed photohydrogen evolution after an anaerobic dark adaptation period. Cultivation of algae in the presence of 100 μm EDTA inhibited the formation of hydrogenase activity by 37%. After a cultivation of the cells in the presence of 5-20 μm NiCl photohydrogen evolution was increased by 20-40% . Addition of EDTA up to a final concentration of 1.5 mᴍ had no effect on the activity of hydrogenase in cell-free hydrogenase preparations. Cultures grown in the presence of radioactive NiCl incorporated Ni in a parallel fashion to the cell growth. In radioactive labeled hydrogenase preparations a co-elution of radioactivity and hydrogenase activity could be observed using gel filtration chromatography.