Regulation of electron transport in isolated chloroplasts by sequential binding of adenine nucleotides to the coupling factor protein

Changes in the ferricyanide-reducing activity in isolated spinach chloroplasts by adenine nucleotides were measured in the presence or absence of phosphate, arsenate or pyrophosphate at 15°C. The activity changes were analyzed and ascribed to the interaction between the nucleotides and the chloroplast coupling factor (CF₁).ADP and ATP (but not AMP) partially inhibited ferricyanide reduction through a 11 binding to the inhibition site on CF₁.When the ferricyanide reduction was coupled to either phosphorylation or arsenylation, the inhibition by ADP was released through a 11 binding of the second ADP molecule to the coupling site on the CF₁ with which the first ADP had been associated.The association constants of ADP for the inhibition and the coupling site were found to be approximately 5×10⁵ and 6×10⁴ M^–1, respectively. TheKm value of ADP for arsenylation (pH 8.3) was around 17 M.The ADP-regulated electron transport was defined based on these results. The ADP-regulated ferricyanide reduction, when coupled with phosphorylation, revealed a stoichiometry of P/e=1 between the amounts of esterified phosphate and reduced ferricyanide.Presented to the annual meeting of the Japanese Society of Plant Physiologists, Sendai, April 1974.