Chemical modifications on proteins can provide significant information about chemical stresses during some physiological events. In this study, we have demonstrated a comprehensive LC/MS/MS-based strategy for screening various chemical modifications of human serum albumin (HSA), the most abundant blood plasma protein. A complementary use of different proteases (trypsin and Glu-C), LC columns (C18 and HILIC), and ion detection modes (positive and negative) improved the number of detected peptides, sequence coverage, and identification of the target modifications. A database search using Mascot or Proteome Discoverer revealed 16 and 13 modifications from HSAs treated by in vitro oxidation and nitration, respectively. A commercially available albumin depletion kit was used to clean up HSA from pooled plasma. The database analysis enabled it to find 7 types of 36 modification sites, including Met87, Trp214, and Cys34 oxidation, and the glycation of Lys525. The differential analysis between the plasma sample and HSA standard using XCMS Online revealed that 13 peptides had more than 3.5-fold changes with p ＜0.05.
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