Serine effects on collision-induced dissociation and photodissociation of peptide cation radicals of the z+•-type

摘要

The serine residue displays specific effects on the dissociations of peptide fragment cation-radicals of the >z^+• type which are produced by electron transfer dissociation. Energy-resolved collision-induced dissociation (ER-CID), time-resolved infrared multiphoton dissociation (TR-IRMPD), and single-photon UV photodissociation at 355 nm revealed several competitive dissociation pathways consisting of loss of OH radical, water, and backbone cleavages occurring at N-terminal and C-terminal positions relative to the serine residue. The activation modes using slow-heating and UV photon absorption resulted in different relative intensities of fragment ions. This indicated that the dissociations proceeded through several channels with different energy-dependent kinetics. The experimental data were interpreted with the help of electron structure calculations that provided fully optimized structures and relative energies for cis and trans amide isomers of the >z4^+• ions as well as isomerization, dissociation, and transition state energies. UV photon absorption by the >z4^+• ions was due to Cα-radical amide groups created by ETD that provided a newchromophore absorbing at 355 nm.