Total Ion Chromatogram (TIC) and MS/MS spectra showing the site- specific identification of esterified glutamic acid residues within the tryptic peptide HC 263–281.

Abstract

(A) Total Ion Chromatogram showing distinct esterification peaks with identical m/z eluting prior to the unmodified peptide peak. (B) MS/MS spectrum of E279 esterification within the tryptic peptide HC 263–281. Despite sharing an identical parent mass, this peptide possesses a distinct y4+ -y5+ ion series compared to the E276 esterified residue in HC 263–281 (Fig 2B).</p