Figure 3

Two consecutive stages of mass spectrometric fragmentation (MS³). The precursor of peptide DVPNSQPEMVEAVK (a; see insert) was selected for fragmentation from a full scan of mass to charge ratio range. The doubly charged y₁₂ fragment ion (b) was subsequently fragmented. Characteristic pattern for charged directed fragmentation is observed in MS³ spectra (c) and confirms the identification of the above peptide. See Steen and Mann [65] for an introduction to peptide sequencing and confidence of peptide identification. MS, mass spectrometry.