Light-induced ATP Formation from Acetyl Phosphate and ADP by Broken Spinach Chloroplasts

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Spinach chloroplasts catalyzed ATP formation from acetyl phosphate and ADP when exposed to light. No ATP formation was detectable in the dark. In the absence of ADP, chloroplasts did not hydrolyze acetyl phosphate in the light or dark. Neither high-energy phosphates such as creatine phosphate and phosphoenol pyruvate nor inhibitors of photophosphorylation competitive with P_i, such as β-naphthyl monophosphate, phenyl phosphate and pyridoxal 5-phosphate, could substitute for acetyl phosphate as a P_i donor. The apparent K_m values for acetyl phosphate and P_i were 0.81 m_M and 0.25 m_M, respectively. The maximal rate of ATP formation with acetyl phosphate and P_i were 331 and 521 μmol ATP formed mg chl^<-1> hr^<-1>, respectively. The optimum pH value for acetyl phosphate-dependent ATP formation was about 8.0. NH_4Cl, di-cyclohexylcarbodiimide and triphenyltin chloride inhibited the acetyl phosphate-dependent ATP formation. Acid-base transition also could induce subsequent ATP formation from acetyl phosphate and ADP. These results suggest that the acetyl phosphate-dependent ATP formation requires the formation and the utilization of a proton-motive force as ordinary photophosphorylation does.
日本植物生理学会の論文