Figure 5.

Selected spectra of compound–peptide adducts detected by peptide mass spectrometry. Prototype compounds were incubated with purified proteins from the Rtt109 HTS, and then samples were subjected to LC-MS/MS analyses after in-gel proteolysis. Shown are peptide MS/MS spectra with assigned y- and b-type fragments. (A) Compound 1a forms a detectable adduct with C94 on yeast Rtt109. (B) Compound 6a forms a detectable adduct with mono-oxidized C21 on yeast Vps75. Shown in each spectra are the sequences for the precursor peptide and a simplified reaction scheme for the adduct formation. See Supporting Information, Table S3, for additional examples of compound–peptide adducts detected by peptide mass spectrometry.