Site-specific uncoupling of photosynthetic phosphorylation in spinach chloroplasts.

In spinach chloroplasts which have been shaken with n-heptane, photophosphorylation coupled to the reduction of nicotinamide adenine dinucleotide phosphate is inhibited about 95% while the photoreduction of NADP+ (and ferricyanide) is stimulated as much as 50%. Photophosphorylation catalyzed by phenazine methosulfate, however, is inhibited only 50%. These data are interpreted to indicate that there are two sites of photophosphorylation in spinach chloroplasts. Both sites are utilized in cyclic photophosphorylation, whereas one of the sites is common to both cyclic and noncyclic photophosphorylation. In heptanetreated chloroplasts the only site functioning is that site associated exclusively with cyclic electron flow. Heptane treatment also has a differential effect upon the adenosine triphosphatase activities of chloroplasts. Trypsinactivated Ca++-dependent ATPase is not aftected by heptane treatment, whereas Mg++-dependent ATPase activated by light in the presence of dithiothreitol is inhibited 80 to 90%. After heptane treatment, the ability of chloroplasts to accumulate protons upon illumination is inhibited 40 to 60% and their ability to synthesize ATP when transferred from acidic to alkaline environment is inhibited 50%.