Figure 2.

QTRP for pairwise quantitation of –SH levels (Fu et al., 2017, 2020). Cys –SH in protein lysates are labeled by IPM, unlike oxidized Cys thiols (SOX, bold red font). After trypsin digestion, IPM-tagged Cys are differentially conjugated with light (orange) or heavy (brown) isotope-labeled Az-UV-biotin depending on the conditions (for instance, H₂O₂-treated versus nontreated cells). After mixing light- and heavy-tagged samples, biotinylated peptides are captured on streptavidin and modified peptides are photoreleased by 365-nm UV light. Eluted peptides are identified and quantified by MS analysis. Comparison of peptide precursor intensities allows deduction of relative –SH levels between conditions. I, intensity; RT, retention time; SOX, oxidized thiol.