Modulation of cytochrome c-membrane interaction by the physical state of the membrane and the redox state of cytochrome c

Association of cytochrome c with anionic membranes involved both electrosta tic and hydrophobic interactions and their relative contributions depended on the physical stair of the membrane and the redox state of cytochrome c. Hydrophobic interaction was favored by the membranes in gel phase, by the m embranes with a large curvature, and by the membranes with a high surface c harge density. Ferrocytochrome c was less dissociable by NaCl than ferricyt ochrome c suggesting that a lower protein stability is beneficial for hydro phobic interaction. Hydrophobic interaction induced larger structural pertu rbations on cytochrome c as monitored by the loss of the Fe-Met bond and by the increase in the distance between heme and Trp-59. When bound to anioni c membranes, spin-labeled cytochrome c showed an electron paramagnetic reso nance spectrum with two or more components, providing a direct evidence fur multiple conformations of bound cytochrome c.