Figure 5.

HNE modified WRN was characterized by LC-MS-MS/MS analysis. (A) Fragmentation spectrum of the DNVAVMATGYGK peptide—modified at Lys577. (B) Fragmentation spectrum of the NPQITCTGFDRPNLYLEVR peptide—modified at Cys727. During fragmentation, the peptide dissociates into two fragments. Fragments containing the N-terminal part of the peptides are termed b series ions (singly ‘b’ and doubly ‘b++’ charged), and, respectively, fragments containing the C-terminal part are named y series ions (singly ‘y’ and doubly ‘y++’ charged) (51). Tables represent a list of theoretical fragment ions calculated by the Mascot program, which served to identify modified peptide (fragment ions found in the spectra are shadowed). Assignment of dominating peaks from the spectra to the theoretical fragmentation ions definitely confirms the modification.