Collision‐induced dissociations of deprotonated peptides. Dipeptides containing methionine or cysteine

The collisional activation mass spectra of the [M – H]− ions of dipeptides containing Met or Cys show the usual backbone fragmentation allowing the sequence of the peptide to be determined. A methionine residue may be identified by the presence of a pronounced peak resulting from loss of MeSH, while a cysteine residue may be identified by the presence of a peak corresponding to loss of either H2S or (H2S + CO2).