Preferential cleavage of S S and C S bonds in electron detachment dissociation and infrared multiphoton dissociation of disulfide-linked peptide anions

Disulfide bonds generally show only limited cleavage in positive ion mode collision activated dissociation (CAD). However, it has been emonstrated that a reverse situation exists in negative ion mode in which preferential S S and C S bond cleavage occurs. Here, we show that lectron detachment dissociation (EDD) and infrared multiphoton dissociation (IRMPD) of peptide anions containing disulfide linkages also result n preferential cleavage of S S and C S bonds. Resulting products are mainly radical ions in EDD whereas IRMPD produces even-electron roduct ions, as expected, thereby supporting different disulfide cleavage mechanisms for these two fragmentation processes. We also show that, n EDD, the presence of tryptophan can result in abundant side chain loss (129 Da), which effectively can compete with disulfide bond cleavage. 2007 Elsevier B.V. All rights reserved.