Bioenergetics Studies of the Cyanobacterium Anabaena variabilis

A cell-free system exhibiting both photophosphorylation (P /2e = 1) and oxidative phosphoryla­ tion (P/O up to 0 .8 ) is described for the cyanobacterium Anabaena variabilis. NADH and N A D PH were found to be equally effective as electron donors for oxidative phosphorylation. Low concentrations of U H D B T , an inhibitor of the cytochrome blc complex of mitochondria and chloroplasts. were found to inhibit photosystem-II electron transport reactions, but did not affect the cytochrom e b6//-com plex of Anabaena. The inhibition by mvxothiazol, antimycin and heptylhydroxyquinoline corroborates the hypothesis that the cytochrom e ö6//-com plex.