Energy-linked reactions in photosynthetic bacteria: Pi in equilibrium with HOH oxygen exchange catalyzed by the membrane-bound inorganic pyrophosphatase of Rhodospirillum rubrum

The inorganic phosphate-water oxygen exchange reaction has been studied in chromatophores of Rhodospirillum rubrum. Under appropriate conditions, chromatophores catalyzed this exchange at a rate of up to 150 μatom oxygen/h/mg bacteriochlorophyll. The reaction is largely inhibited by inhibitors of the membrane-bound inorganic pyrophosphatase, fluoride and methylene diphosphonate, and is not inhibited by oligomycin. These results indicate that the P_i ? HOH oxygen exchange is almost entirely due to the pyrophosphatase. In the presence of ADP, the exchange reaction was stimulated by about 40% and this portion of the exchange was sensitive to oligomycin, but not to fluoride or methylene diphosphonate. Thus this portion of the exchange can be attributed to the ATP synthese complex. The rates of the oxygen exchange reaction and other chromatophore-catyalyzed reactions are compared.