Interaction of synthetic fragments of the extension peptide of cytochrome P-450(SCC) precursor with phospholipid bilayer

: Six peptide fragments, SEP6-11, SEP6-15, SEP1-11, SEP1-15, SEP1-20, and SEP25-39, corresponding to the residues 6-11, 6-15, 1-11, 1-15, 1-20, and 25-39, respectively, of the extension peptide of cytochrome P-450(SCC) precursor were chemically synthesized by the solution method. CD spectra of the peptides indicated that SEP1-15 and SEP1-20, which inhibit the import of the precursor, held a random conformation in a Tris-HCl buffer and a partially ordered conformation (like alpha-helix or type II' beta-turn) in a buffer containing acidic liposomes. Slightly changed spectra were observed for SEP1-15 and SEP1-20 in the buffer containing neutral liposomes and in MeOH, respectively. Other peptides which show weak or no inhibitory effect had almost random conformations in these solvents. The hydrophobic moments of SEP1-15 and SEP1-20 when they take alpha-helical conformation are very small, suggesting that amphiphilic helical property is not always necessary for the import of the precursor, although partially ordered conformation seems to be required. The ability of SEP1-15 and SEP1-20 to induce leakage of carboxyfluorescein from the inside of dipalmitoyl-DL-alpha-phosphatidylcholine (DPPC) or DPPC-dipalmitoyl-DL-alpha-phosphatidylglycerol (3:1) vesicles was much greater than that of other peptides. The leakage induction ability of the peptides qualitatively parallels the degree of their inhibition of the import of the precursor. Perturbation of the membranes caused by the action of the peptides in their partially ordered form may be important for the import of the precursor into mitochondria.