Fig. 1

LC–MS/MS Quantification of Cys-277 sulfenylation. Recombinant Src (∼0.6 µg/µL) was either incubated with 1.0 mM of light dimedone (dim-d₀) in the absence of H₂O₂ or treated with 1.0 mM H₂O₂ in the presence of 1.0 mM heavy dimedone (dim-d₆) to trap sulfenylated cysteine residues. Equal amounts of dim-d₀ and dim-d₆ Src were combined prior to trypsin digestion and LC–MS/MS analysis. a Representative MS1 spectrum exhibiting peaks corresponding to the dim-d₀- (m/z 1119.5, inset) and dim-d₆-conjugated (m/z 1122.5) Cys-277 containing peptide fragment LGQGCFGEVWMGTWNGTTR (2+ charge). b Representative extracted ion chromatograms (with deuterated version eluting slightly earlier) from peptide-targeted parallel reaction monitoring (PRM) of dim-d₀ (black, relative intensity multiplied by ten) and dim-d₆ (red) enabling the determination of relative amounts of dim-d₆/dim-d₀ corresponding to a heavy to light (H/L) ratio of 78.57 ± 5.54 (triplicate analysis). H/L ratio was calculated from the five transitions from three experimental replicates