Radiation chemical studies of Gly-Met-Gly in aqueous solution

Abstract

Important biological consequences are related to the reaction of HO^• radicals with methionine (Met). Several fundamental aspects remain to be defined when Met is an amino acid residue incorporated in the interior of peptides and proteins. The present study focuses on Gly-Met-Gly, the simplest peptide where Met is not a terminal residue. The reactions of HO^• with Gly-Met-Gly and its N-acetyl derivative were studied by pulse radiolysis technique. The transient absorption spectra were resolved into contributions from specific components of radical intermediates. Moreover, a detailed product analysis is provided for the first time for Met-containing peptides in radiolytic studies to support the mechanistic proposal. By parallel radiolytical and electrochemical reactions and consequent product identification, the formation of sulfoxide attributed to the direct HO^• radical attack on the sulfide functionality of the Met residue could be excluded, with the in situ generated hydrogen peroxide responsible for this oxidation. LC–MS and high resolution MS/MS were powerful analytical tools to envisage the structures of five products, thus allowing to complete the mechanistic picture of the overall Met-containing peptide reactivity.

Keywords:

• Methionine
• free radicals
• peptide
• ionizing radiation
• electrochemistry
• EC-MS
• LC–MS/MS
• reaction mechanism

Acknowledgements

All authors gratefully acknowledge the support and networking opportunities they received from COST Action CM1201 on “Biomimetic Radical Chemistry”. One of us (KB) would like to thank Professor Ian Carmichael for his hospitality during the stay. This is document number NDRL-5130 from the Notre Dame Radiation Laboratory.

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.