EFFECTS OF PLASTOCYANIN ON PHOTOPHOSPHORYLATION

1. 1. A simplified procedure for the large-scale isolation and purification of plastocyanin from spinach chloroplasts is reported. After electrophoresis on polyacrylamide gel, a pure protein was obtained as judged by analytical gel electrophoresis and by the fact that it contained no arginine. 2. 2. Plastocyanin from spinach or cytochrome c552 from Euglena stimulated the photoreduction of NADP+ in subchloroplast particles prepared by prolonged exposure of chloroplasts to sonic oscillation. 3. 3. Photophosphorylation in the presence of pyocyanine or NADP+ was enhanced by plastocyanin and cytochrome c552 whereas ferricyanide- or N-methylphenazonium methosulfate-dependent phosphorylation was not. Dichlorophenyldimethylurea abolished cyclic phosphorylation with pyocyanine and with N-methylphenazonium methosulfate in red light. This inhibitor had much less effect on phosphorylation in the presence of partially reduced pyocyanine or N-methylphenazonium methosulfate in white light. 4. 4. Coupling factors 1 and 2 were required for optimal rates of pyocyanine- or NADP+-dependent phosphorylation. © 1969.