Interaction of a coupling factor from Rhodospirillum rubrum with coupling factor deficient chromatophores

A coupling factor necessary for the photophosphorylation and Mg²⁺-ATPase activities of Rhodospirillum rubrum chromatophores has been separated from these particles. Although the redox potential of coupling factor deficient chromatophores is slightly more oxidized than of the control, the addition of the coupling factor for reconstitution does not alter the redox potential. Phenazine methosulfate cannot restore or significantly enhance the photophosphorylation activities of uncoupled or reconstituted chromatophores compared to the control. The coupling factor can bind to coupling factor deficient membranes without addition of magnesium ions and thus restore the photophosphorylation and Mg²⁺-ATPase activities of these vesicles. The Ca²⁺-ATPase in the coupling factor preparation shows binding characteristics similar to those of the coupling factor.