title: Electron capture dissociation initiates a free radical reaction cascade.
abstract: For small cyclic peptides, one electron capture by the [M + 2H](2+) ion generates numerous fragments corresponding to amino acid losses, side-chain losses, and losses of some low molecular weight species such as H(2)O, CH(3)(*), C(3)H(6), and (*)CONH(2). As predicted, the side-chain cleavages are amplified relative to linear peptides of similar size, but the amino acid losses were unexpected because they require that one electron capture cause more than one backbone cleavage, a phenomenon which necessitates further refinement or reinterpretation of current ECD mechanisms. A modified mechanism is postulated in which nonergodic electron capture fragmentation generates an alpha-carbon radical species that then propagates along the protein backbone. This radical migration initiates multiple free radical rearrangements, which cause both multiple backbone cleavages and additional side-chain cleavages.
authors.affiliation: Department of Biochemistry, Boston University School of Medicine, 715 Albany Street, R806, Boston, Massachusetts 02118, USA.
authors.forename: Nancy
authors.initials: N
authors.lastname: Leymarie
authors.forename: Catherine E
authors.initials: CE
authors.lastname: Costello
authors.forename: Peter B
authors.initials: PB
authors.lastname: O'Connor
mesh_terms: D000595:Amino Acid Sequence; D016572:Cyclosporine / Q000737:chemistry; D005609:Free Radicals / Q000737:chemistry; D006096:Gramicidin / Q000737:chemistry; D013058:Mass Spectrometry; D010456:Peptides, Cyclic / Q000737:chemistry*
chemical_list: D005609:Free Radicals; D010456:Peptides, Cyclic; D006096:Gramicidin; D016572:Cyclosporine