Influence of charge state and amino acid composition on hydrogen transfer in electron capture dissociation of peptides.

Although conventional N-Cα bond cleavage in electron capture dissociation (ECD) of multiply-charged peptides generates a complementary c' and z(·) fragment pair, the N-Cα cleavage followed by hydrogen transfer from c' to z(·) fragments produces other fragments, namely c(·) and z'. In this study, the influence of charge state and amino acid composition on hydrogen transfer in ECD is described using sets of peptides. Hydrogen transferred ionic species such as c(·) and z' were observed in ECD spectra of doubly-protonated peptides, while the triply-protonated form did not demonstrate hydrogen transfer. The extent of hydrogen transfer in ECD of doubly-protonated peptides was dependent on constituent amino acids. The ECD of doubly-protonated peptides possessing numerous basic sites showed extensive hydrogen transfer compared with ECD of less basic peptides. The extent of hydrogen transfer is discussed from the viewpoints of the structure of peptide ions, the possibility of internal hydrogen bonding and intermediate lifetime of complex [c' + z(·)].