Effects of permeant buffers on the initial time course of photophosphorylation and postillumination phosphorylation.

Permeant buffers (pyridine, imidazole, or phosphate) caused similar increases in the time required for onset of ATP synthesis in the light in the presence of valinomycin and K+; and in the illumination time required for postillumination phosphorylation with or without or without valinomycin and K+. Based on prior evidence, the minimum illumination time required for postillumination phosphorylation in thylakoid membranes is taken as a measure of the time required for formation of a transmembrane pH gradient sufficient to drive ATP synthesis. Our results are consistent with the view that, following illumination, as the transient transmembrane electric gradient decays, the establishment and maintenance of a pH gradient serves for energy transfer from the photosystems to the ATP synthase complex.