Ultraviolet photodissociation of protonated, fixed charge, and charge-reduced peptides

Abstract

The fragmentation behavior of three peptides (RGAFSTFGAS, GAFSTFGASR, and GAFSTFGASS) was evaluated by collisional activated dissociation (CAD), higher energy collisional activated dissociation (HCD), and ultraviolet photodissociation (UVPD). In particular, hybrid methods combining electron transfer with CAD, HCD, or UVPD were used to assess the impact of the location of a basic site at the C- or N-terminus, the presence of a fixed charge at the C- or N-terminus, and the presence of a radical site. The release of a mobilized proton occurred for those peptides modified with a quaternary amine at the C- or N-terminus, thus resulting in formation of C- and/or N-terminus fragment ions that would not otherwise be expected if the fixed charge remained static. Activation of charge-reduced peptides (i.e. peptide radical ions) resulted in simplified spectra compared to the corresponding even electron peptides. Interestingly, UVPD of the charge-reduced species generated similar spectra to CAD and HCD of the same precursor ions, suggesting a shift to dominant radical-induced dissociation rather than the more diverse pathways common upon photodissociation.