Figure 5.

Representative MALDI-TOF-MS spectrum of derivatized N-glycans released from total plasma (TPNG) using 6-Cl-HOBt as catalyst at native conditions, and linkage-specificity of the reaction conditions as determined on a TPNG sample. (A) Mass spectrum showing relative intensities from m/z 1000 to 3700. Compositional assignments were based on accurate mass and isotopic pattern matching, structural assignments were based on literature and biosynthetic pathways. Except for the N-acetylneuraminic acids, glycosidic linkages were not determined. The assigned glycan signals had a signal-to-noise (S/N) > 9. Different sialic acid linkages are indicated by a left (α2,3) or right (α2,6) angle. (B) Relative ratio of di- and triantennary sialylated species with the gross composition hexose (H)5; N-acetylhexosamine (N)4; N-acetylneuraminic acids (S)2; and H6N5S3 and their different sialic acid linkage variants (lactonized α2,3-sialic acid: L; ethyl esterified α2,6-sialic acid: E) after incubation with the different catalysts under native and acidic pH at 37 °C. Note: the di- and triantennary glycans are total area normalized to 100% separately. Error bars represent SD for triplicate measurements.