Changes in Internal Hydrogen Ion Concentration Associated with Photophosphorylation in Intact and Sonically Treated Chloroplasts

By using different pH indicators it is possible to demonstrate, in the presence or absence of phosphorylation, the existence of two compartments in chloroplasts, one of which becomes more acidic and the other more basic during electron flow. The observed magnitude of the pH differential between these two compartments is over 1.5 pH units. Cations, such as NH4+, N-methylphenazonium methosulfate, and protonated neutral red, which compete with H+ ions for entry into chloroplasts, inhibit the development of pH gradients within chloroplasts. Diffusible anions, such as acetate and orthophosphate, also block formation of these internal pH gradients. All of the above inhibitors of formation of internal pH gradients also inhibit phosphorylation, in a parallel manner. Sonic treatment of chloroplasts causes progressive and parallel inhibition of phosphorylation and formation of internal pH gradients. These data support the concept that chloroplasts contain a proton-translocating oxidation-reduction chain and that the resultant efflux of H+ ions through chloroplast membranes supplies the energy for phosphorylation.