Anion-dependent changes of energy transfer in chloroplasts I. Effects of Tris salts on electron flow and phosphorylation

Washing spinach chloroplasts with high-concentration Tris-saltbuffers induced various types of anion-dependent changes inthe electron flow and photophosphorylation in chloroplasts. Tris-HCl buffer caused enhancement of NADP photoreduction andinhibition of phosphorylation. Tris-HNO₃ buffer, on the otherhand, caused inhibition of both electron flow and phosphorylationand decreased trypsin-activated Ca²+-dependent ATPase activity.Tris-H₂SO⁴ and Tris-H₃PO⁴ buffers, however, had no effect onthe rates of electron flow and photophosphorylation. Determination of the presence of the coupling factor (as measuredby ATPase activity) revealed a normal enzyme activity levelin chloroplasts washed with Tris-HCl or Tris-H₂SO⁴ buffer. Removalof the coupling factor by EDTA from chloroplasts washed withTris salts inhibited phosphorylation severely. Phosphorylationactivity could be partially restored by reconstitution withthe coupling factor in die presence of Mg²+. In addition to their different effects on electron flow, Tris-HCland Tris-HNO₃ induced a marked decrease in phosphorylative activityitself. The much decreased rate of phosphorylation can be explainedby the release of the coupling factor and by damage to the high-energystate generating mechanism by Tris-HNO₃-washing and by modificationof the coupling factor in the case of Tris-HCl-washing. ¹Present address: Biology Department, College of Science andEngineering, Ryukyu University, Naha, Okinawa. Japan. (Received June 27, 1972; )