Generation of Semiquinone and Oxygen Radicals by the Reaction of Menadione with Reduced Glutathione at Various pH

Abstract

Semiquinone radicals of menadione were generated during the reaction of menadione with reduced glutathione (GSH), dependent upon the pH. Under aerobic conditions, cytochrome c was reduced during the reaction, and superoxide dismutase (SOD) inhibited the cytochrome c reduction. The inhibitory effect of SOD was greater at a high pH than at a low pH. In the presence of Fe³⁺ or ethylenediaminetetraacetic acid (EDTA)-Fe³⁺, deoxyribose was degraded during the reaction of menadione with GSH, dependent upon the pH. Greater amounts of deoxyribose were degraded at a low pH than at a high pH. The reduction of Fe³⁺ of EDTA-Fe³⁺ also depended on the pH, and SOD strongly inhibited the Fe³⁺ reduction, indicating that Fe³⁺ or Fe³⁺-EDTA was reduced by superoxide. SOD, catalase, mennitol and benzoate inhibited the deoxyribose degradation at various pH values. These results indicate that the menadione semiquinone radical is readily formed at an alkali pH but a hydroxyl radical is predominantly produced near a neutral pH. A hydroxyl radical may be generated via an iron-catalyzed Haber-Weiss reaction.