LC-MS/MS Analysis: Purified phosphopeptide samples were reconstituted in 4 ml buffer A (0.1% FA in H 2 O) and analyzed by LC-Q-TOF MS (Waters Q-TOFTM Premier from Waters Corp). For LC-MS/MS analysis by Waters Q-TOFTM Premier, samples were injected into a 2 cm6180 mm capillary trap column and separated by 20 cm675 mm Waters1 ACQUITYTM 1.7 mm BEH C18 column using a nanoACQUITY Ultra Performance LCTM system (Waters Corp). The column was maintained at 35uC and eluted with a linear gradient of 0-80% buffer B (0.1% FA in ACN) for 80, 120, 210 and 270 min. MS was operated in ESI positive V mode with a resolving power of 10,000. NanoLockSpray source was used for accurate mass measurement and the lock mass channel was sampled every 30 s. The mass spectrometer was calibrated with a synthetic human [Glu1]-Fibrinopeptide B solution (1 pmol/ml; Sigma) delivered through the NanoLockSpray source. Data acquisition was operated in the data directed analysis (DDA). The method included a full MS scan (m/z 400-1600, 0.6 s) and 3 MS/MS (m/z 100-1990, 1.2 s each scan) sequentially on the most three intense ions present in the full scan mass spectrum.