COLLISION-INDUCED DISSOCIATION AND POST-SOURCE DECAY OF MODEL DODECAPEPTIDE IONS CONTAINING LYSINE AND GLYCINE

Collision-induced dissociation (CID) and post-source decay (PSD) of a series of model dodecapeptide ions have been studied by ESI-FT-ICR and MALDI-TOF, respectively. Low-energy CID of quadruply protonated pepti de ions, [M + 4H](4+), where M = (KGG)(4), (K(2)G(4))(2), and K(4)G(8) , was conducted under both on-resonance irradiation and sustained off- resonance irradiation (SORI) conditions. The fragmentation patterns ob served were very sequence dependent. For (KGG)(4), the major product i ons involved y-cleavages occurring on the C-terminal side of the lysin e residues. These dissociation sites and the correspond ing charge sta tes of the product ions can be explained on the basis of the four prot ons being primarily localized on lysine residues. For (K(2)G(4))(2), b oth Y and b series ions were observed as dissociation products. The ob servation of b ions in the vicinity of the C-terminus is not consisten t with the model of protons being localized on lysine residues. The da ta suggest that, during the CID process, protons may migrate to the le ss basic C-terminal glycine residue in order to minimize Coulomb repul sion. This is also supported by CID studies of K(4)G(8) where the majo r dissociation products are b type ions formed from cleavages near the C-terminus. In contrast with the CID results, PSD of [M + H](+) from all three peptides leads to formation of almost complete series of y a nd b type ions, with cleavages at the lysine residues often being most prominent. In summary, it was found that low-energy CID of [M + 4H](4 +) in an ESI-FT-ICR yielded pronounced cleavages at the basic lysine r esidues, which may provide information about the number and locations of basic residues; however, PSD of [M + H](+) in a MALDI-TOF provided a wider range of fragment ions that should prove useful in peptide seq uencing. (C) 1997 Elsevier Science B.V.