Heatmap summarizing temporal profiles of 23 selected phosphopeptides. PRM (left) and iTRAQ-based (right) temporal phosphorylation profiles are depicted. Phosphopeptides were clustered according to their PRM profiles, the PRM color code represents log2-fold changes compared with controls. In 7 cases, the corresponding quantitative value was missing for the iTRAQ data (black). Notably, the lower precision of iTRAQ-based quantification leads to ratio compression. Therefore, the smaller scale of iTRAQ ratios was adjusted to the PRM measurements to facilitate the visual comparison (ie, iTRAQ log2-ratios ranged from −1.2 to 2.8). In most cases, the overall phosphorylation changes could be confirmed using an alternative quantification method, additional donors, and platelet preparations conducted by different coworkers.