Interaction of cytochrome c with cardiolipin: an infrared spectroscopic study.

The interactions of cytochrome c (cyt c) with cardiolipin, a major anionic phospholipid of mitochondrial membranes, and dioleoylphosphatidylglycerol (DOPG), have been compared by infrared (IR) spectroscopy. The Fourier self-deconvoluted IR spectra of the lipid carbonyl groups indicate that both cyt c3+ and cyt c2+ perturb and/or dehydrate the interfacial region of cardiolipin bilayers. Only a slight perturbation, if any, is observed in the interfacial region of DOPG bilayers. However, the phosphate head region of DOPG is perturbed by cyt c3+, which was not detected in cardiolipin. The results suggest that cytochrome c in both redox states can partially penetrate into cardiolipin but not into DOPG bilayers. The interaction of cyt c with cardiolipin and DOPG is mainly hydrophobic and electrostatic, respectively. The Fourier self-deconvoluted IR spectra in the amide I region reveal that ca. 10% of the cyt c3+ alpha-helix unfolds to random coil upon binding to cardiolipin bilayers. However, only very slight secondary structural changes, if any, were detected when cyt c3+ binds to DOPG bilayers.