Abstract
The primary structure of the membranous segment of porcine liver microsomal cytochrome b5 was determined. This polypeptide was at the COOH terminus of the cytochrome molecule and consisted of 43 amino acids. It was essential for the insertion of the cytochrome into the endoplasmic reticular membrane. Automated sequence analysis of tryptic and CNBr/anhydrous heptafluorobutyric acid peptides provided data from which the following unique amino acid sequence was deduced: Ile-Ala-Lys-Pro-Ser-Glu-Thr-Leu-Ile-Thr-Thr-Val-Glu-Ser-Asn-Ser-Ser-Trp-Trp-Thr-Asn-Trp-Val-Ile-Pro-Ala-Ile-Ser-Ala-Leu-Val-Val-Ser-Leu-Met-Tyr-His-Phe-Tyr-Thr-Ser-Glu-Asn. A prediction of .alpha.-helices, .beta.-structures and .beta.-turns based on the sequence of this polypeptide was presented.