C‐terminal sequencing of protein

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Abstract
Peptides or proteins were hydrolyzed by vapors of 90% pentafluoropropionic acid or heptafluorobutyric acid at 90°C for various time periods. The hydrolyzate mixtures analyzed by both fast‐atom‐bombardment and electrospray ionization mass spectrometry showed a series of C‐terminal successive degradation molecular ions. The degradation reaction may be due to the selective formation of an oxazolone ring at the C‐terminal amino acid, followed by hydrolytic removal of the C‐terminal amino acid. The major side reactions were cleavages of the peptide bonds at the C side of the internal aspartic acid residue and the N side of serine residue.