Fig. 3.

A Gaussian line shape fitted to the individual isotopologue peaks to determine N-glycan occupancy. This MS1 spectrum shows the N169-containing peptide from the CD16a V158 allotype, following PNGaseF-catalyzed N-glycan removal in [¹⁶O]-water. The major peak in the upper left panel contains only an unglycosylated Asn at position 169. The major peak in the upper middle panel contains contributions for both Asn and Asp (formed by PNGaseF digestion of an N-glycosylated peptide) at this position, with the Asp-containing peptide predominant in this example.