INTERACTION BETWEEN CYTOCHROME C AND PURIFIED PHOSPHOLIPIDS

Isooctane-soluble complexes formed between cytochrome c and various mixtures of phosphatidylserine and phosphatidylcholine have been studied, with the following results. 1. 1. For a given phospholipid mixture there is a unique total lipid to protein ratio for maximum complex extraction. 2. 2. At maximum extraction, each cytochrome c molecule binds 9 molecules of phosphatidylserine and 5-60 molecules of phosphatidylcholine according to the composition of the original phospholipid mixture. When the phosphatidylserine to cytochrome c ratio exceeds 9:1, decreased extraction of both lipid and protein is observed. 3. 3. Other saturated paraffins exhibit similar bahaviour to isooctane, but unsaturated, or halogenated hydrocarbons, do not extract complexes under similar conditions. 4. 4. In 100 mM NaCl, each cytochrome c molecule is associated with 70-100 phosphatidylserine molecules, and a maximum of 400-500 phosphatidylcholine molecules. The results suggest an electrostatic interaction between the phosphatidylserine and protein. The mode of binding of the phosphatidylcholine is not clear. © 1969.