Immunochemical characterization of steroid hydroxylases of adrenocortical mitochondria. 2. Localization of antigenic determinants in the cytochrome P450scc molecule (CYP11A1).

The antigenic structure of cytochrome P450scc was investigated by immunochemical identification of the peptides formed by chymotryptic cleavage of the protein and separated by reversed-phase and cation-exchange HPLCs. These procedures resulted in isolation and structural characterization of four homogeneous immunoreactive peptides which corresponded to the sequences Asn236-Tyr241, Leu266-Leu272, Ala381-Phe388, and Ser390-Trp400. These peptides contained several positively charged residues which were previously shown to participate in electrostatic interactions with adrenodoxin. Our data indicate that the positively charged residues of cytochrome P450scc are involved in formation of antigenic sites, and the antigenic determinants of the protein molecule coincide or overlap with the regions of polypeptide chain responsible for the interaction of the heme protein with adrenodoxin.