Fig. 3.

Examples of two glycopeptide MS/MS spectra. A, complex, monosialylated, and difucosylated N-glycan is observed; B, complex monosialylated N-glycan is observed. Fragment ions are observed as a series of Y-type ions from the intact N-glycopeptide precursor and a clear sequential loss of the N-linked core mannoses and N-acetylglucosamine. In each case, a ^0,2X₀ type cleavage is observed for the reducing end N-acetylglucosamine. Remaining glycan compositions are assigned by accurate mass losses from the precursor ion, and a minimum of four Y- or X-type ions was required for each assignment. Although full structural characterization was not performed, a possible glycan is shown for each spectrum that reflects the composition determined. The full set of assignments is shown in Table III.