Cleavage of cytochrome c with cyanogen bromide

Abstract

Heme peptides and nonheme peptides suitable for use in binding studies have been prepared by cleavage of horse cytochrome c with cyanogen bromide. These derivatives include a heme peptide of 65 residues and a peptide of 39 residues obtained by division of the protein at the bond following methionine residue 65. Other useful products include: (1) a peptide corresponding to residues 66–104 of the parent molecule, but with a homoserine residue substituted for the methionine residue in position 80; (2) smaller peptides consisting of residues 66–80 and 81–104; and (3) a heme peptide of 80 residues containing a homoserine instead of a methionine residue in position 65. Unlike other instances in which conversion of a methionine to a homoserine residue has been observed to occur without peptide-bond cleavage, neither of the methionine residues of horse cytochrome c is followed by a threonine or serine residue. A mechanism similar to that for the hydrolysis of N-phenyliminolactone is proposed.