Fig. 5.

An example of a disulfide bridge. (a and b) are the tandem mass spectra of a same peptide sequence IVSNASCTTNCLAPLAK, but the former one is with two carbamidomethylated cysteines, while the latter one has a disulfide bridge across the two cysteines. The spectrum in (a) has several product ions indicating the CID fragmentations between the two cysteines, while in (b) no noticeable ions supporting such fragmentations can be found in the query spectrum identified with the ΔM of −116.06 Da. Most of intensive peaks are explained with low m/z errors.