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. Author manuscript; available in PMC: 2020 Jul 2.
Published in final edited form as: Anal Chem. 2019 Jun 13;91(13):8516–8523. doi: 10.1021/acs.analchem.9b01732

Figure 1.

Figure 1.

DEPC labeling of model peptides. Extracted ion chromatograms (XICs, left) of the +1 ions of the unmodified and DEPC-modified peptides Fmoc-DGXGG-amide, where X is a DEPC modifiable residue (a) Ser, (b) Thr, (c) Tyr, (d) His, or (e) Lys, after allowing the peptide to react with DEPC at a DEPC:peptide molar ratio of 5:1. Modification percentages are calculated from peak areas in XICs. Tandem mass spectra acquired after CID of the labeled precursor ions are used to confirm the site of modification. MS/MS assignments of the modified peptides are shown in Figure S2. Note that two chromatographic peaks for the labeled peptide in (d) are observed because the His side chain has two nitrogens that are separately labeled to produce isomers that can be separated by LC.