The invariant ARG91 is required for the rupture of liposomes by cytochrome C

Lipid binding properties of cytochrome c (cyt c) were investigated by using semisynthetic mutant protein having amino acid substitution on the evolutionary invariant residue Arg91. We demonstrate here that the membrane binding properties of cyt c are dramatically altered by substituting norleucine for the invariant Arg91. More specifically, while the binding of this mutant to liposomes per se is indistinguishable from the wild type protein, it completely lacks the ability of the native cyt c to rupture liposome bilayers.