Figure 2

Example fragmentation spectra of a PGHS-1 N -glycosylation site containing peptide TGFYGENCSTPEFLTR, indicating variable glycosylation. High mass accuracy of precursor peptides combined with MS/MS fragment ions readily captures expected ¹⁶O/¹⁸O dependent mass-shifts and confidently identifies that the site has variable glycosylation state in the recombinant protein. y-series fragment ions which pinpoint the modification within the sequence are indicated with red arrows (note, that beyond y9-fragment the masses are shifted relative to the unmodified fragments according to the incorporated oxygen atom).