Fig. 1.

MS/MS spectra with site determining ions for top two site localizations (matched peaks only). Black peaks are shard ions, while red and blue ones are the site determining ions for each site localization. The two site localizations are shown in the text in the upper left corner of each panel (lower case indicates PTM sites). (a) Peptide with a low score due to lack of clear site determining ions. (b) Peptide with a high score with evidence for both localizations, indicating the possibility of co-eluting positional isomers