Identification of the C-terminal amino acid amides by carboxypeptidase Y digestion and fast atom bombardment mass spectrometry.

The combination method of carboxypeptidase Y digestion and fast atom bombardment (FAB) mass spectrometry is described for the identification of C-terminal amino acid amides in peptides. Carboxypeptidase Y has amidase activity as well as exopeptidase activity in the same digestion buffer condition. Based on this concept, we develop a new technique which can definitively and easily identify the C-terminal amino acid amides. This method obviates the need for several complicated steps occurring in previous methods, but improves sensitivity, and enables exact identification of the amino acid amide by the difference of molecular mass. Analyses of carboxypeptidase Y digested peptides, not liberated free amino acid amides, were carried out by fast atom bombardment mass spectrometry. The use of truncated peptides by fast atom bombardment mass spectrometry in C-terminal amino acid amide determination gives several advantages over analyses of the liberated amino acid amides. The C-terminal amino acid amides of Allantostatin I (Leu-NH2), alpha-Melanocyte Stimulating Hormone (Val-NH2), and Ranatensin (Met-NH2) are unequivocally determined at a level of 0.90-2.3 nmol per peptide. This approach is based on entirely different principles than the previous approaches.