SMALL-ANGLE X-RAY SCATTERING STUDIES OF CYTOCHROME C-PHOSPHOLIPID COMPLEXES

Cytochrome c in water and isooctane-soluble lipid-protein complexes formed between cytochrome c and a mixture of natural phospholipids (phosphatidylcholine/phosphatidylserine) has been studied by small angle X-ray scattering methods. In the concentration range corresponding to 0.04%-1.00% cytochrome c in isooctane, two distinct types of isooctane-soluble complex with radii of gyration of 66 A and 87 A are observed, whilst in water, cytochrome c has a radius of gyration of 12-14 A. The large radii of gyration and sedimentation coefficients suggested by ultracentrifugation studies show that the complexes in isooctane cannot consist simply of 20:1 or 30:1 lipid-protein monomeric units, but molecular aggregation occurs (particle weight > 1 000 000). © 1969.