Gas-phase fragmentation of long-lived cysteine radical cations formed via no loss from protonated S-nitrosocysteine

  • Victor Ryzhov
  • Adrian K. Y. Lam
  • Richard A. J. O’Hair
Focus: Ion-Surface Collisions And Peptide Radical Cations

DOI: 10.1016/j.jasms.2008.12.026

Cite this article as:
Ryzhov, V., Lam, A.K.Y. & O’Hair, R.A.J. J Am Soc Mass Spectrom (2009) 20: 985. doi:10.1016/j.jasms.2008.12.026

Abstract

In this work, we describe two different methods for generating protonated S-nitrosocysteine in the gas phase. The first method involves a gas-phase reaction of protonated cysteine with t-butylnitrite, while the second method uses a solution-based transnitrosylation reaction of cysteine with S-nitrosoglutathione followed by transfer of the resulting S-nitrosocysteine into the gas phase by electrospray ionization mass spectrometry (ESI-MS). Independent of the way it was formed, protonated S-nitrosocysteine readily fragments via bond homolysis to form a long-lived radical cation of cysteine (Cys•+), which fragments under collision-induced dissociation (CID) conditions via losses in the following relative abundance order: •COOH ≫ CH2S > •CH2SH-H2S. Deuterium labeling experiments were performed to study the mechanisms leading to these pathways. DFT calculations were also used to probe aspects of the fragmentation of protonated S-nitrosocysteine and the radical cation of cysteine. NO loss is found to be the lowest energy channel for the former ion, while the initially formed distonic Cys•+ with a sulfur radical site undergoes proton and/or H atom transfer reactions that precede the losses of CH2S, •COOH, •CH2SH, and H2S.

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Copyright information

© American Society for Mass Spectrometry 2009

Authors and Affiliations

  • Victor Ryzhov
    • 1
  • Adrian K. Y. Lam
    • 2
    • 3
    • 4
  • Richard A. J. O’Hair
    • 2
    • 3
    • 4
  1. 1.Department of Chemistry and BiochemistryNorthern Illinois UniversityDeKalbUSA
  2. 2.School of ChemistryThe University of MelbourneMelbourneAustralia
  3. 3.Bio21 Institute of Molecular Science and BiotechnologyThe University of MelbourneMelbourneAustralia
  4. 4.AR Centre of Excellence for Free Radical Chemistry and Biotechnology, School of ChemistryUniversity of MelbourneParkvilleAustralia