Enzymatically digested samples were diluted in 0.1% formic acid (1:5, v/v) and analyzed by LC–MS/MS. LC–MS/MS experiments were performed on a Dionex U3000 LC system coupled to a qExactive mass spectrometer, both from Thermo Scientific (San Jose, CA, USA). Chromatographic separation was performed on a Zorbax SB-C18 column (150×2.1mmi.d., 5 μmparticle size, 300 Å porosity) fromAgilent Technology (Palo Alto, CA, USA). Peptides from BSA were eluted from the column at a flow rate of 200 μl/min using water as mobile phase A and acetonitrile as mobile phase B, both containing 0.1% formic acid. A fast linear gradient from 5 to 60% B in 8 min was performed. Then the column was washed for 2 min at 95% B. The equilibration time before the next analysis was set at 5 min, so that the time between two experimental cycles was 15 min. Column temperature was maintained at 60 °C. The column effluentwas directly introduced into the electrospray source of the qExactive mass spectrometer. Analyseswere performed in the positive ion mode, and sequential MS2 experiments were performed using the data-dependent acquisition method. The five most abundant precursor ions (charge states higher than +1) were selected for fragmentation using higher energy collisional dissociation (HCD).