Fig. 8.

Phosphorylcholine is a modification of O-glycans from Caenorhabditis elegans. Negative-mode LC–ESI–MS/MS analyses indicate the occurrence of five O-glycan structures carrying HexNAc₁PC₁ motifs. The fragment ions at [M-H-59]⁻ or [M-H-N(CH₃)₃]⁻ are diagnostic for phosphocholine containing glycans and arise by loss of the trimethylamine group. Z fragment ions containing subterminal hexuronic acid residues are often accompanied by loss of the carboxyl group [Z-CO₂]⁻ (A and C), a characteristic absent from MS/MS of glycans with nonreducing hexuronic acid (B). As for N-glycans, HexNAc₂PC_1–2 motifs exist as nonreducing terminal modifications of O-glycans (D and E). For MS/MS of selected neutral O-glycans, refer to supplemental Fig. S13. ESI, electrospray ionization.