Figure 4. MS² spectra of the ions at m/z 2,042.6, 2,245.0, 2,406.3, 2,608.6, 2,770.1, 2,972.6 and 3,134.2.

Ion peaks derived from the MS spectrum of tryptic MT1-FLAG digests at m/z 2,042.6, 2,245.0, 2,406.3, 2,608.6, 2,770.1, 2,972.6 and 3,134.2 (Fig. 3) were subjected to MS² analysis. These fragment ions were assigned to the loss of single monosaccharides (162 and 203 Da for Hex and HexNAc, respectively) from the same peptide ion (²⁹⁹TTSRPSVPD³⁰⁷).