RECOGNITION OF THE CARBOXY-TERMINAL PEPTIDE IN CYANOGEN-BROMIDE DIGESTS OF PROTEINS

A method is reported that allows carboxy-terminal peptides to be recog nized in cyanogen bromide cleavage reactions. Recognition is based on mass spectrometric analysis of the peptide products before and after r eaction with acidic methanol. Peptides generated from internal positio ns in the protein are terminated by homoserine lactone, which undergoe s methanolysis to add 32 mass units. The peptide containing the origin al carboxyl terminus is converted to a methyl ester, with a mass incre ment of 14 Da.