PROTON LOCATIONS IN DOUBLY CHARGED PEPTIDES AND ASSOCIATION WITH SPECIFIC FRAGMENTATION PATHWAYS

Abstract Mass-analyzed ion kinetic energy (MIKE) spectrometry has been employed to measure intercharge distances in the doubly protonated octapeptide PPGFSPFR. The interpretation of the experimental observations, aided by macromolecular mechanics calculations, suggests that two isomeric forms of the doubly charged ions are produced by both FAB and electrospray, which differ from each other by the location of one of the protons. Different fragmentation pathways are shown to occur in each of these isomers. This is interpreted following the mechanism of Adams et al., J. Am. Soc. Mass Spectrom., 7 (1996) 30.