Structural and sequence effects in the fragmentation of protonated tripeptides containing tyrosine

Abstract

The fragmentation reactions of a variety of protonated tripeptides containing tyrosine in the three possible positions have been studied by energy-resolved collision-induced dissociation mass spectrometry. The primary fragmentation reactions involve cleavage of the N-terminal and (or) C-terminal amide bond with the relative importance of the two cleavages depending strongly on the identity and position of the amino acid residues in the tripeptide. The results are interpreted in terms of the a1–y mechanism for cleavage of the N-terminal amide bond and the bx–yz mechanism for cleavage of the C-terminal amide bond and, indeed, provide support for these mechanisms. However, it appears likely that, for protonated H-Val-Tyr-Pro-OH, the neutral accompanying formation of the y1 (protonated proline) ion is a cyclic dipeptide (cyclo-Val-Tyr) rather than the oxazolone predicted by the bx–yz mechanism.Key words: tyrosine-containing peptides, fragmentation mechanisms, tandem mass spectrometry.