Tandem mass spectrometry (MSn) and collision induced dissociation (CID) are among the most important tools used to identify peptides and proteins in proteomics. Fragmentation of gas-phase, protonated peptides creates product ions that reveal amino acid sequence. Recently we found that conversion of peptides to N-terminal imines (as Schiff bases) enhances the sequence information revealed by the MSn approach. More remarkably, we found that dissociation of Ag+ cationized versions of these peptide-imines creates never-before seen (M-H)+ ions (essentially peptide carbocations) by loss of AgH. The MSn fragmentation of these ions provides important sequence information as well. In this presentation, the preparation of the peptide-imines will be described, as well as the generation of the carbocations and their CID behavior. Of particular importance is the comparison of the fragmentation of the carbocations to protonated peptide imines and to protonated peptides that lack the imine group.

Peptide sequencing using gas-phase peptide carbocations

249th National Meeting (2015)

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