The reconstitution of photophosphorylation and the effect of inorganic phosphate at different pH's on the phenazine methosulfate photoinhibition of Rhodospirillum rubrum chromatophores

Preillumination of R. rubrum membranes in the presence of 50M phenazine methosulfate produces an inhibition of their photophosphorylating capacity.At low pH's phosphate protects against this photo-inhibition, whereas increasing the pH eliminates this protective effect. The inhibition can be produced not only by preillumination at high pH in the presence of phenazine methosulfate, but also by preillumination at low pH (5.0) and then shifting the pH to 8.0 in the dark. We have also measured the effect of preillumination in the presence of an uncoupler such as carbonylcyanide p-trifluoromethoxyphenylhydrazone, and found that at normal pH's while photophosphorylation was protected, the uncoupler activated ATPase was inhibited pointing to a clear difference for both reactions and perhaps different structural requirements for their activities.The purified coupling factor protein isolated from either normal or photoinactivated membrane will reconstitute normal photophosphorylation in previously uncoupled membranes but not in uncoupled membranes which were inactivated by preillumination with phenazine methosulfate prior to uncoupling.