DEPENDENCE OF H-2380( EXCHANGE AND OXYGEN EVOLUTION ON K+ IN THE MARINE CYANOBACTERIUM SYNECHOCOCCUS SP STRAIN UTEX)

Light-induced net H+ efflux, photosynthetic oxygen evolution, and medi um alkalization during the steady state of photosynthesis were specifi cally stimulated by K+ from pH 6 through 8.5 in the marine cyanobacter ium Synechococcus sp. strain UTEX 2380. Net proton efflux in the light was completely abolished by the uncoupler carbonylcyanide m-chlorophe nylhydrazone and the membrane ATPase inhibitor diethylstilbestrol or p artially abolished by the membrane ATPase inhibitor N,N'-dicyclohexyl carbodiimide and by orthovanadate. H+ extrusion in the light was accom panied by K+ uptake at rates of 30 mu mol.mg chlorophyll(-1). h(-1). D uring the steady state of CO2 fixation, potassium was excreted simulta neously with medium alkalization. The K+ content of the cells was 432 mM for air-grown cells. K+ in the cells was displaced by diethanolamin e, which was inhibited by m-chlorophenylhydrazone. Nae-loaded cells sh owed nearly complete inactivation of oxygen evolution and medium alkal ization. Both activities were reactivated by the addition of K+ or Rb. A fivefold increase in inorganic carbon uptake in the light was obse rved in the presence of K+. The pH of the cytoplasm in the light incre ased from 7.2 to 8.04 in the pH range 6.6-8.6. These results suggest t hat a light-dependent, proton-excreting ATPase is active in conjunctio n with a K+ uptake system in a marine Synechococcus species, while a K +-H+ antiporter may function as a regulator of cytoplasmic pH during p hotosynthesis.