Long-lived electron capture dissociation product ions experience radical migration via hydrogen abstraction.
To explore the mechanism of electron capture dissociation (ECD) of linear peptides, a set of 16-mer peptides were synthesized with deuterium labeled on the alpha-carbon position of four glycines. The ECD spectra of these peptides showed that such peptides exhibit a preference for the radical to migrate to the alpha-carbon position on glycine via hydrogen (or deuterium) abstraction before the final cleavage and generation of the detected product ions. The data show c-type fragment ions, ions corresponding to the radical cation of the c-type fragments, c*, and they also show c*-1 peaks in the deuterated peptides only. The presence of the c*-1 peaks is best explained by radical-mediated scrambling of the deuterium atoms in the long-lived, metastable, radical intermediate complex formed by initial electron capture, followed by dissociation of the complex. These data suggest the presence of at least two mechanisms, one slow, one fast. The abundance of H* and -CO losses from the precursor ion changed upon deuterium labeling indicating the presence of a kinetic isotope effect, which suggests that the values reported here represent an underestimation of radical migration and H/D scrambling in the observed fragments.
O'Connor
Peter B
PB
Mass Spectrometry Resource, Department of Biochemistry, Boston University School of Medicine, 670 Albany St., Rm. 507, 02118, Boston, MA, USA. poconnor@bu.edu.
Lin
Cheng
C
Mass Spectrometry Resource, Department of Biochemistry, Boston University School of Medicine, 670 Albany St., Rm. 507, 02118, Boston, MA, USA.
Cournoyer
Jason J
JJ
Mass Spectrometry Resource, Department of Biochemistry, Boston University School of Medicine, 670 Albany St., Rm. 507, 02118, Boston, MA, USA.
Pittman
Jason L
JL
Mass Spectrometry Resource, Department of Biochemistry, Boston University School of Medicine, 670 Albany St., Rm. 507, 02118, Boston, MA, USA.
Belyayev
Marina
M
Mass Spectrometry Resource, Department of Biochemistry, Boston University School of Medicine, 670 Albany St., Rm. 507, 02118, Boston, MA, USA.
Budnik
Bogdan A
BA
Mass Spectrometry Resource, Department of Biochemistry, Boston University School of Medicine, 670 Albany St., Rm. 507, 02118, Boston, MA, USA.
D000595:Amino Acid Sequence; D003903:Deuterium; D005609:Free Radicals / Q000737:chemistry; D005998:Glycine / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry; D013058:Mass Spectrometry / Q000379:methods*; D015394:Molecular Structure; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*
D005609:Free Radicals; D010455:Peptides; D006859:Hydrogen; D003903:Deuterium; D005998:Glycine