Application of iTRAQ Reagents to Relatively Quantify the Reversible Redox State of Cysteine Residues
Figure 3
Fragmentation spectrum of peptide 40YSGVCHTDLHAWHGDWPLPTK60 with iTRAQ reporter ions magnified. (a) Reporter ions 114 and 118 are for controls and indicate approximately half of this Cys population is in a free thiol state. After exposure to 1 mM H2O2, there is a decrease in reporter ion 116 for total free thiols and reporter 121 indicates that it is predominantly reversibly oxidized and not present as a free thiol. (b) Reporter ions 114 and 118 are again controls and are equivalent to the control results in (a), that is, approximately half of the Cys in the peptide are in the free thiol form. After exposure to 5 mM H2O2, there is a dramatic reduction in reversibly oxidized thiols (reporter 121) indicating, at this concentration, that the Cys residue is susceptible to irreversible oxidation.
