[Different types of interaction of oxidized and reduced cytochrome c with phospholipid vesicles]

The binding constants of ferri- and ferrocytochrome c interactions with phosphatidylcholine or cardiolipin-containing vesicules were determined. It was found that affinity of ferricytochrome c to phospholipids is one order of magnitude higher that of ferrocytochrome c. A comparative investigation of circular dichroism spectra of free and phospholipid-bound ferri- and ferrocytochrome c was undertaken and it was shown that alpha-helix content of free ferrocytochrome c is higher than that of ferricytochrome c. The formation of ferricytochrome c containing lipoprotein complex led to decrease of alpha-helix content of the protein. In the case of ferrocytochrome c on the other hand interaction with phospholipids did not cause any changes in alpha-helix content. Distribution of ferri- and ferrocytochrome c in different two-phase systems consisting of dextran and polyethylenglycol or dextran and polyethylenglvcol-palmitate was also studied. A comparison of distribution constants shows that higher alpha-helix content of ferrocytochrome c results in the formation of hydrophobic clusters in the protein molecules. In previous communications it was reported that binding of ferrocytochrome c to phospholipids is determined by hydrophobic interactions while in the case of ferricytochrome c the interactions with phospholipids are mainly electrostatic. On the basis of the results obtained in this work it is supposed that it is hydrophobic clusters which determine the binding of ferrocytochrome c to phospholipid membranes.