Charge dependence of protonated insulin decompositions

Abstract

Ion trap collisional activation is used to study the effects of charge state on protonated insulin decompositions for three forms of insulin: bovine, porcine, and human. Tandem mass spectrometry data are presented for ions with one to five protons dissociated under identical resonance excitation conditions. The (M+5H) 5+ and (M+4H) 4+ ions fragment exclusively by peptide bond cleavage of bonds outside the cycles formed by the disulfide linkages present in the insulin molecule, whereas the (M+3H) 3+ and (M+2H) 2+ ions appear to show a mixture of peptide bond cleavage and fragments arising from mechanisms associated with disulfide bond cleavage. The (M+H) + ion fragments almost exclusively by way of disulfide bond cleavage, with the only major exception being cleavage on the C-terminal side of glutamic acid residues external to the cycles formed by the disulfide linkages.