Isolation and identification of C-terminal peptides of proteins

A method for the isolation and identification of C-terminal peptides of proteins has been developed. The procedure entails the racemization of the C-terminal amino acid by reaction of the N-trifluoroacetylated protein with acetic anhydride and pyridine. After deprotection, the protein is fragmented to yield a mixture of peptides, which in turn are digested with carboxypeptidases. All peptides are hydrolyzed to L-amino acids except the C-terminal peptide with the terminal D-amino-acid residue. It is resistant to the action of carboxypeptidases and is readily identified by peptide mapping.