Fig. 2.

Peptides containing alkylated and oxidized cysteine, identified in plasma data, and an MS/MS spectrum. C* represents carbamidomethylated cysteine. In the spectrum, ions that are not generated by peptide backbone fragmentation are observed at 703 and 1078 m/z. The ions are produced by the loss of ROSH (R = alkylation derivative) and are spaced by 107 Da in case of R = carbamidomethyl. These are the evidence for the existence of alkylated and oxidized cysteine, but it becomes the dominant fragmentation pathway, resulting in a low quality MS/MS spectrum.