Fig. 1

O-GlcNAc site information is lost before peptide backbone fragmentation. CAD MS/MS spectrum of GlcNAcylated peptide (YSPTgSPSK, [M+GlcNAc+2H]²⁺ 535.2) showing a major peak [M+H]⁺ 866.3 corresponding to loss of GlcNAc