An investigation of dipeptides containing polar and nonpolar side groups by curie-point pyrolysis tandem mass spectrometry.

Methionyl-leucine, leucyl-methionine, phenylalanyl-leucine, and leucyl-phenylalanine have been analyzed to determine dipeptide fragmentation mechanisms in Curie-point pyrolysis tandem mass spectrometry. Results show that fragmentations of dipeptides follow two general pathways, one involving direct cleavage of the dipeptide and the other involving cyclization of the dipeptide. Unique products and strong changes in relative mass spectral peak intensities arise, depending on constituent amino acid residues and their sequence. Also, the length and nature of the side groups strongly direct fragmentation. From these results, the major peaks in the spectra of eight other dipeptides could be readily explained; this suggests that a significant number of dipeptides follow the same general fragmentation mechanisms.