Validation of quantification results for kinases obtained from the PRM-based targeted proteomic method. (a) Representative PRM traces for peptides from targeted kinases. Listed are the PRM traces of IGQPTLLLYVDAGPETMTQR from AK1 (y5, y6, y7, y8, y9, y10), SCSPSAEFLR from JAK3 (y3, y5, y6, y7, y8), NTSTMIGAGSK from PAK1 (y5, y6, y7, y8, y9), MTDEEIMEK from PAK2 (y3, y4, y5, y6, y7, y8), VILPQVLLGLR from SCYL3 (y4, y5, y6, y7, y8, y9) and SIAVAEAACPGITDK from STK26 (y3, y6, y7, y8, y9, y11). The y ions listed in the parentheses were the fragment ions observed in the MS/MS of the corresponding peptides that were chosen for peptide quantification. (b) Western blot for the validation of the expression levels of representative kinases in paired primary/metastatic melanoma cells. (c) Quantitative comparisons of ratios of kinase protein expression obtained from PRM (c) and Western blot (d) analyses. The data represent the mean ± S. D. of the quantification results (n = 3). The uncropped images for Western blot are provided in supporting information file.