Radical Scavenging by Thiols and the Fate of Thiyl Radicals

Abstract

Reduced glutathione reacts rapidly with the majority of biological free radicals and is regarded as a good radical scavenging antioxidant. However, the reaction generates thiyl radicals, which are strong, potentially damaging oxidants that need to be removed for the process to be effective. Sequential reactions of the radical with the thiolate anion and oxygen drive the scavenging reaction, producing the disulfide and superoxide radicals. Protein thiols are also good radical scavengers via a similar mechanism, and this is an efficient route for generating intramolecular disulfides, mixed disulfides with glutathione and nitrosothiols. These interactions are relevant not only to antioxidant defence but as part of a network of radical reactions that can regulate the oxidation state of glutathione and the extent of protein S-thiolation as well as acting as a source of superoxide and hydrogen peroxide. This chapter discusses the radical chemistry of glutathione and other thiols and how it could contribute to redox activity in the cell.