Figure 2: Representative spectra of Ser/Thr phosphopeptide ELVEPLpTPSGEAPNQALLR in EGFR protein (A) and Tyr phosphopeptide IADPEHDHTGFLTEpYVATR in MAPK3 protein (B). In the MS/MS analysis, b and y ions of various peptides were detected and the localization of the phosphorylation sites were determined by PTM scores in MSQuant software analysis as described previously (Olsen et al., 2006). The matched b and y ions for a given phosphopeptide sequence are colored red and blue, respectively.