Cytochrome c redox state influences the binding and release of cytochrome c in model membranes and in brain mitochondria

Cytochrome c (cyt c), a component of the respiratory chain, promotes apoptosis when released into the cytosol. Cyt c anchorage within mitochondria depends on cardiolipin (CL). Detachment and release have been related to CL loss and peroxidation. We report that NaN3- dependent complex IV inhibition, accompanied by impairment of respiration, resulted in cyt c release. Contrarily, inhibition of respiration upstream cyt c with complex I and III inhibitors was not accompanied by the release of the protein, despite CL decrease and monolyso-CL increase. No CL changes and H2O2 formation were observed by inhibiting complex IV. In cyt c–CL liposomes, breaching cyt c–CL hydrophilic interactions produced a higher release of the reduced, compared to the oxidized form, suggesting that the hydrophobic component of cyt c–CL binding is prevalent in the oxidized form. Free or liposome-reconstituted cyt c was able to form fatty acid–protein complexes (palmitate\linoleate\oleate) only in its reduced form. We hypothesize that reduced cyt c–fatty acid binding favors the dislocation of the protein from anchoring CL. A mechanism for cyt c release independent of CL peroxidation by H2O2 is feasible. It could weaken the hydrophobic component of cyt c–CL interactions and might function following complex IV inhibition or in oxygen lack, both conditions producing accumulation of reduced cyt c and free fatty acids.