Cyanogen Bromide Fragments of Human Serum Albumin

Abstract

CNBr cleaves nonreduced human serum albumin into three large fragments, A, B, and C, which account for the total amino acid composition of albumin. Reduction and carboxamidomethylation of the free —SH groups produce four subfragments from A, identified according to their NH₂-terminal amino acid residues as A-ProI (32 residues), A-AsxI (38 residues), A-ProII (109 residues), and A-Phe (92 residues). A small residue which contains no homoserine is unaccounted for in this sum of the subfragments in A. A-AsxI contains the COOH-terminal leucine of albumin. Reduction and carboxamidomethylation of fragment B produce two further subfragments, B-Ala (36 residues) and B-AspII (89 residues). These subfractions account for all amino acid residues in B. B-AspII contains the NH₂-terminal Asp and free —SH group of albumin. Fragment C has only one peptide chain (164 residues) with an NH₂-terminal Cys residue. Heterogeneity in disulfide linkages is evident in some preparations.