Assignment of all of these structural features has motivated exploration of other ion activation methods, such as ultraviolet photodissociation (UVPD). In addition to generating fragment ions suitable for determining the peptide sequence (a, b, c, x, y, and z ions), including glycosite-localizing ions that retain the glycan, UVPD promotes cross-ring cleavages (A/X ions) of the saccharides that are instrumental for identifying the positions of the glycosidic bonds between saccharides. A difference in linkage position can have profound effects on protein function, its recognition of other cells, disease progression, and is imperative for understanding disease pathology. Therefore, the combination of mucinase proteolysis and UVPD offers a compelling strategy to advance characterization of O-glycoproteins, as detailed in this study.