Fig 4. Analysis of the N-terminal peptides of the secreted and ER-retained mAbs by mass spectrometry.

A) MS/MS spectrum of the pQ₂₀VQLVESGGGVVQPGRSLR₃₈ peptide from the heavy chain ([M+2H]²⁺ precursor ion at m/z 796.92). B) MS/MS spectrum of the E₂₃IVMTQSPATLSVSPGER₄₀ from the light chain ([M+2H]²⁺ precursor ion at m/z 951.48). C) MS/MS spectrum of the TLSVSPGER from the light chain (M+2H]²⁺ precursor ion at m/z 473.25). pQ is indicated a N-terminal pyroglutamine residue formed by cyclisation of glucosamine. For all spectra, Y and B ions have been identified and allowed peptide sequencing.