Mass spectrometric identification of amino acid thiohydantoins

Amino acid thiohydantoins were identified using electron impact and chemical ionization mass spectrometry. Some fragmentations of thiohydantoin ring were also identified. These results suggest that the thiohydantoin method should be useful for the stepwise peptide sequence analysis starting from the carboxyl terminus. The sequence of a model tripeptide was determined by the combination of the thiohydantoin method and mass spectrometry. In the case of peptide which contained a proline residue as their C-terminal peptide, cleavage of the peptide bond cannot be achieved.