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

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Washing spinach chloroplasts with high-concentration Tris-salt buffers induced various types of anion-dependent changes in the electron flow and photophosphorylation in chloroplasts. Tris-HCl buffer caused enhancement of NADP photoreduction and inhibition of phosphorylation. Tris-HNO_3 buffer, on the other hand, caused inhibition of both electron flow and phosphorylation and decreased trypsin-activated Ca^<2+> -dependent ATPase activity. Tris-H_2SO_4 and Tris-H_3PO_4 buffers, however, had no effect on the rates of electron flow and photophosphorylation. Determination of the presence of the coupling factor (as measured by ATPase activity) revealed a normal enzyme activity level in chloroplasts washed with Tris-HCl or Tris-H_2SO_4 buffer. Removal of the coupling factor by EDTA from chloroplasts washed with Tris salts inhibited phosphorylation severely. Phosphorylation activity could be partially restored by reconstitution with the coupling factor in the presence of Mg^<2+>. In addition to their different effects on electron flow. Tris-HCl and Tris-HNO_3 induced a marked decrease in phosphorylative activity itself. The much decreased rate of phosphorylation can. be explained by the release of the coupling factor and by damage to the high-energy state generating mechanism by Tris-HNO_3-washing and by modification of the coupling factor in the case of Tris-HCl-washing.
日本植物生理学会の論文