Cytochrome b5 from a Normal Human Liver

A cytochrome b5 was isolated from an individual human liver and found to have some 50 additional terminal residues more than previously reported in this protein from human sources. The tryptic digest of this preparation was characterized, and a chromatography system was devised to resolve all of the tryptic peptides by a single colume procedure. The sequence previously established for the human protein is identical with the segment comprised of residues 5 to 92 of the larger cytochrome. The largest cytochrome b5 whose primary structure is known is that of the rabbit. Comparison between this and the human protein shows the human cytochrome to be 4 residues longer at the NH2 terminus and to extend some 37 residues at the COOH terminus. The methods of investigation developed in this study will be helpful in determining how variant cytochrome b5 is in man.