LC-MS/MS analysis of Control, PAR1-stimulated and PAR4-stimulated platelet lysate digests. Control lysate digest peptides were labeled with "light", PAR1 lysate digest peptides were labeled with "intermediate" and PAR4 lysate digest peptides were labeled with "high" dimethyl labeled. Labeled digests were mixed in a 1:1:1 ratio, separated by SCX and the resulting (phosphopeptide-enriched) peptide fractions were analyzed by LC-MS/MS.