Abstract: Collision energy and fragmentation pathways of doubly- and triply-protonated peptide RRMKWKK upon low-energy collision-induced dissociation(CID) were investigated with ESI-MS/MS. Triply-protonated ion dissociated more easily than the doubly-protonated ion, with a dependence of the number of charges vs. the number of the arginine residues in the peptide. The two basic Arg residues were the primary charge location, resulted in a high dissociation energy for Arg-contained peptides. The protonated ions with one more proton than the number of Arg residues in the peptides were suggested when Arg-containing peptides were studied by using mass spectroscopy. Secondary structures of the protonated RRMKWKK calculated by AM1 method indicate that the two protons locating at the basic side chains of the two adjacent Arg were separated in space, so that Coulomb repulsion did not affect the proton location.

Key words: Arginine residue, Fragmentation location site, Collision-induced dissociation, Collision energy