Previously uncharacterized ions observed in the high energy collision-induced dissociation mass spectra of peptides containing S-alkyl cysteine

Abstract

The high-energy collision-induced dissociation (CID) spectra of a number of peptides containing S-β-(4-pyridylethyl)-, S-carbamidomethyl- and S-carboxymethylcysteine have been generated and several hitherto undescribed fragmentation pathways identified. For peptides containing pyridylethylcysteine at the nth position, these include x n − 105, a n+1 + 1 − 106, a n+1 + 1 − 138, z n+1 + 1 − 106, z n+1 + 1 − 138, and combined side chain loss ions. The analogous fragment ions were also observed in the spectra of peptides containing other S-alkylcysteines. Also, two fragmentations unique to pyridylethylcysteine-containing peptides, resulting in the formation of b n+ ≥ 1 - R C + H and CO + peC ions, were studied. Precursor scanning, exact mass measurement and CID of the appropriate source-generated fragment ions have been employed to identify the origin of these ions and to facilitate the proposal of mechanisms for their formation.