HCD MS/MS spectrum (@ 30V) of a tryptic glycopeptide of Gp20 shows near saturation of consecutive Thr residues with the O-HexNAc modification.

The precursor ion [M + 4H]4+ m/z 1001.9305 has a monoisotopic mass corresponding to that calculated for the peptide


plus seven HexNAc residues (Δ 0.5 ppm). There is a prominent HexNAc oxonium ion (m/z 204.0868) and full series of b and y ions, some of which contain one (*) or two (**) HexNAc residues. All ions are singly charged, except where indicated. In addition, charge-reduced ions, all 2+, which correspond to species that have undergone consecutive losses of HexNAc residues, are labeled as follows: ‡** = [M + 2H]2+—HexNAc5 (m/z 1495.1470), ‡* = [M + 2H]2+—HexNAc6 (m/z 1393.6224), ‡ = [M + 2H]2+ aglycon peptide (m/z 1292.0851).