PRIMARY STRUCTURE OF THE MEMBRANE-BINDING SEGMENT OF RABBIT CYTOCHROME-B5

The primary structure of the membrane-binding segment of rabbit cytochrome b5 has been determined. This segment, prepared by trypsin digestion of the intact protein, consists of 43 amino acid residues and corresponds to the COOH-terminal end (residues 91-133) of the parent molecule. Deduction of the primary structure was based on automated sequence analysis of the whole segment as well as manual and dansyl-Edman degradations of peptide fragments produced by CNBr cleavage and partial acid hydrolysis. The sequence obtained is: Leu -Ser -Lys -Pro -Met -Glu -Thr -Leu -He -Thr-Thr-Val-Asn-Ser-Asn-Ser-Ser-Trp-Trp-Thr -Asn-Trp-Val-Ile-Pro-Ala-Le-Ser-Ala-Leu-Ile-Val-Ala-Leu-Met-Tyr-Arg-Leu-Tyr-Met-Ala-Asp-Asp. This sequence is 63 to 81% homologous with respect to those determined for the membrane-binding segments of equine, porcine and bovine cytochrome ob5. The interaction of this segment with phospholipid bilayer membranes is discussed, and a prediction of its secondary structure is also presented. © 1979, by the Japanese Biochemical Society.