Simultaneous analysis of C-terminal amino acid residues of peptide mixtures by combination of field desorption mass spectrometry and carboxypeptidase digestion

A novel method is described for the simultaneous analysis of C-terminal amino acid residues of peptide mixtures by combination of field desorption mass spectrometry and carboxypeptidase digestion. The method involves measurement of the mass values of quasi-molecular ions ([M + H]+) of peptides and their digested fragments. The amino acid residues can be determined from the mass differences of the mass values observed in the field desorption mass spectra during digestion of peptides. As typical examples, the simultaneous determinations of the C-terminal amino acid residues of peptide mixtures prepared by tryptic digestion of β-endorphin and parathyroid peptide are described.