30 µg proteins per sample were reduced (20 mM DTT Sigma, room temperature RT, 1 h) and S-alkylated (50 mM IAA Sigma, 1 h, dark). The remaining IAA was quenched with 20 mM DTT for 1 h in the dark. The proteins were digested with 1:50(w/w enzyme:protein) MS-grade trypsin/lys-C mix (Thermo Scientific) for 24 h at RT. The enzyme digestion was quenched by lowering the pH with formic acid (Fisher) and the sample was desalted with ZipTip C18 (Merck-Millipore) column. Samples were resuspended in 10 µl of 0.2% formic acid prior LC-MS/MS analysis.