Figure 4.

Phosphorylation of the Xyl phosphate (a) The extracted ion chromatograms for the [M + 3H]³⁺, [M + Na + 2H]³⁺, [M + 2Na + H]³⁺, and [M + 3Na]³⁺ precursors of the mono-sulfated and the phosphorylated glycoforms of the bikunin 6-mer CS-glycopeptide. The 36.4- and 36.8-min elution time-points are indicated. (b) The HCD spectrum, at m/z 1000–1500, of the mono-sulfated (S-form) precursor, and (c) the HCD spectrum of the phosphorylated (P-form). The NCE was 20%. The full m/z 100–1500 HCD spectrum of the [M + Na + 2H]³⁺ is displayed in Figure 3c. The deduced glycopeptide structures are shown boxed. All major fragment ions are annotated with charges >1, m/z values, n:o of Na⁺-adducts and glycan structures