What kind of fragments dominate in peptide MS spectra?
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 i
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.