Figure 3.

LC-MS and MS/MS analysis of bisecting GlcNAc-bearing glycopeptides in the brain. (A) MS chromatograms of glycopeptides enriched by E4-PHA lectin from wildtype brain membranes. Base peak chromatogram (upper panel). Extracted ion chromatogram (EIC) for ions with masses calculated as [M + 2H]²⁺ and [M + 3H]³⁺ of a bisecting GlcNAc-bearing glycopeptide derived from synaptophysin is selectively shown (middle and lower panels), which was confirmed by tandem mass spectrometry to be modified with bisecting GlcNAc. (B) Average MS spectrum around the peak (27 min) detected in middle and lower panels of (A). Enlargements show that the monoisotopic ions were the corresponding glycopeptides on accurate mass and charge state. (C) MS/MS spectrum of the [M + 3H]³⁺ parent ion is shown in the lower chromatogram of (A). The N-glycan structure of each peak was deduced as indicated.