ALTERNATIVE CYANIDE-SENSITIVE OXIDASE INTERACTING WITH PHOTOSYNTHESISIN SYNECHOCYSTIS PCC6803 - ANCESTOR OF THE TERMINAL OXIDASE OF CHLORORESPIRATION

Influence of respiration on photosynthesis in Synechocystis PCC6803 wa s studied by measuring the redox transients of cytochrome f (cyt f) up on excitation of the cells with repetitive single turnover flashes. Up on the addition of KCN the flash-induced oxidation of cyt f was increa sed and the rereduction of cyt f(+) was accelerated. Dependence of the se effects on the concentration of KCN clearly demonstrated the existe nce of two cyanide-sensitive oxidases interacting with photosynthesis: cyt aa(3), which was sensitive to low concentrations of cyanide, and an alternative oxidase, which could be suppressed by using greater tha n or equal to 1 mM KCN. The interaction between the photosynthetic and the respiratory electron transport chains was regulated mainly by the activity of the alternative cyanide-sensitive oxidase. The oxidative pathway involving the alternative cyanide-sensitive oxidase was insens itive to salicyl hydroxamic acid and azide. The close resemblance of t he inhibition pattern reported here and that described for chlororespi ration in algae and higher plants strongly suggest that an oxidase of the same type as the alternative cyanide-sensitive oxidase of cyanobac teria functions as a terminal oxidase in chloroplasts.