Radical‐Based Damage of Sulfur‐Containing Amino Acid Residues

Abstract

Abstract The reactions of biologically relevant free radicals with S‐ and Se‐containing amino acids are reviewed with regard to amino acid reactivity, the nature of product radicals, and ensuing radical reactions. Emphasis is placed on the formation and reactions of thiyl and selenyl radicals as well as radical cations from sulfides and selenides. The reactions of thiols with carbon‐centered radicals, superoxide, nitrogen monoxide, nitrogen dioxide, and tyrosyl radicals are covered as well as the reactions of thiyl radicals with oxygen. Reversible intra ‐ and inter molecular hydrogen transfer reactions of thiyl radicals are discussed in view of recent experimental and theoretical data. One‐electron oxidation reactions of sulfides are reviewed especially with regard to the stabilization of sulfide radical cations through heteroatom‐containing substituents, which are present in peptides and proteins. The relevance of these radical reactions for protein oxidation under conditions of oxidative stress is discussed.