Interaction of cytochrome c with reaction centers of Rhodopseudomonas sphaeroides R-26: determination of number of binding sites and dissociation constants by equilibrium dialysis.

The number of binding sites and dissociation constants of cytochrome c (horse heart) and cytochrome c2 (Rhodopseudomonas sphaeroides) to reaction centers of Rhodopseudomonas sphaeroides R-26 was determined by equilibrium dialysis. One binding site was found for both cytochromes. The dissociation constants (10 mM Tris-HCl, pH 8.0) were approximately 0.4 microM and approximately 1.0 microM for cytochrome c and cytochrome C2 respectively. Oxidized and reduced forms of both cytochromes bound to reaction centers with approximately equal affinity.