Figure 2.

Src is exclusively labeled by 15a at cysteine 277. (A) Mass spectra (left) and zero-charge mass spectra (right) of SRC incubated (top) with DMSO or (bottom) with a 10-fold molar excess of 15a for 2 h at 37 °C. Unlabeled protein peaks are indicated with purple glyphs, and 15a modified protein peaks are highlighted with blue glyphs. (B) MS/MS spectrum of the SRC tryptic peptide ²⁷³LGQGC*FGEVWMGTWNGTTR₂₈₇ modified with 15a at Cys 277 (indicated with “*” in the sequence). Ions of type y are indicated with red glyphs. Inhibitor modified ions are labeled with green glyphs.⁴⁰