(A) Heat map showing SILAC ratios (SR) of representative tyrosines competed by fragments and organized by hierarchical clustering. Fragment competition at tyrosine sites was quantified using the area under the curve of MS1 extracted ion chromatograms (EIC) from HHS-482-labelled peptides in DMSO (light, red) versus fragment-treated (heavy, blue) DM93 soluble proteomes. Competitive chemical proteomic studies were performed as shown in Supplementary Figure 3. Tyrosine sites shown are liganded (SR >4) by at least 2 fragments with the number of liganded sites and proteins listed for each molecule. Y-axis lists the protein name and quantified tyrosine site. (B) Representative MS1 EICs of tyrosine sites from quantitative LC-MS chemical proteomics: non-liganded (blue, SR <2), partially-liganded (orange, 2≤ SR ≤4), and liganded (yellow, SR >4). (C) Reactivity of fragments was assessed by comparing the fraction of tyrosine sites competed: non-liganded (blue, SR <2), partially-liganded (orange, 2≤ SR ≤4), and liganded (yellow, SR >4). All data shown are representative of n = 2-3 biologically independent experiments.