Interaction of cytochrome c and its precursor apocytochrome c with various phospholipids.

The effects of cytochrome c and apocytochrome c on the structural properties of various membrane phospholipids in model systems were compared by binding, calorimetric, permeability, P n.m.r. and freeze-fracture experiments. Both cytochrome c and apocytochrome c experience strong interactions only with negatively charged phospholipids; apocytochrome c interacted more strongly than cytochrome c. These interactions are primarily electrostatic but also have a hydrophobic character. Cytochrome c as well as apocytochrome c induces changes in the structure of cardiolipin liposomes as is shown by P n.m.r. and freeze-fracture electron microscopy. Cytochrome c does not affect the bilayer structure of phosphatidylserine. In contrast, interaction of apocytochrome c with this phospholipid results in changes of the P n.m.r. bilayer spectrum of the liposomes and also particles are observed at the fracture faces. The results are discussed in relation to the import of the protein into the mitochondrion.