The effects of plastocyanin on photophosphorylation

Abstract

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 c 552 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 c 552 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.