Practice question

During low-energy collision-induced dissociation of protonated peptides, proton mobility model dictates that proton migrates along backbone and weakens peptide bonds, producing mainly b and y type ions. Among these, y ions containing C-terminal portion often dominate spectra because N-terminal fragments may further fragment or undergo cyclization. C-terminal lysine or arginine in tryptic peptides strongly sequesters proton, enhancing stability of y ions. While a-ions accompany b ions, x-ions are rare in CID, and c/z ions appear in electron-based dissociation methods, making y-ion series most informative for database searching in proteomics experiments.