Fig. 4.

Spectra assignments for glucosylgalactosyl-hydroxylysine containing peptides are reported in (A) COL5A1 peptide GEK††GESGPSGAAGPPGPK (K753) with oxidation of P15 and (B) COL1A2 peptide GFPGTPGLPGFK††GIR (K175) with oxidation of P3, P6, and P9. †† denotes site of modification (Δ 340.10 Da). For y and b ion identifications; † denotes the loss of 162.05 Da (Hex), †† denotes the loss of 324.11 Da (2 Hex), * denotes the loss of NH₃, and ^o denotes the loss of H₂O. Assigning these hexose groups as Hyl O-linked galactose and glucosylgalactose is consistent with the well-characterized modification of fibrillar collagens (75–79). Consistent with this assignment, all modifications are found in the triple helix regions.