Determination of the location of positive charges in gas-phase polypeptide polycations by tandem mass spectrometry

摘要: Abstract Location of protonated sites in electrospray-ionized gas-phase peptides and proteins was performed with tandem mass spectrometry using ion activation by both electron capture dissociation (ECD) collisional (CAD). Charge-carrying were assigned based on the increment charge state fragment ions compared to that previous same series. The property ECD neutralize preferentially least basic site confirmed analysis three thousand spectra doubly charged tryptic peptides. Multiply cations bradykinin, neurotensin melittin studied detail. For n+ precursors, revealed positions (n − 1) most sites, while CAD could principle locate all n charges. However, introduced minimal proton mobilization produced more conclusive data than CAD, for which N- C-terminal often disagreed. Consistent dominance one conformer its preservation ECD, average states complementary fragments almost always added up (n − 1)+, similar figure deviated from n+, indicating extensive isomerization under excitation. bradykinin neurotensin, assignments largely agreement intrinsic basicity respective amino acid residues. higher states, charging at intrinsically as well less residues, attributed sharing other groups due presence secondary order structures this larger polypeptide.