title: Formation of glutathione-conjugated semiquinones by the reaction of quinones with glutathione: an ESR study.
abstract: The nonenzymatic reaction of the cytotoxic compounds menadione (2-methyl-1,4-naphthoquinone) and 1,4-naphthoquinone (a reactive metabolite of 1-naphthol) with reducing agents such as NADPH and glutathione led to the formation of semiquinone-free radicals, which were detected with electron spin resonance spectroscopy. In the presence of glutathione as a reducing agent, menadione and 1,4-naphthoquinone underwent net one-electron reduction and conjugation with glutathione. At higher concentrations of glutathione, 1,4-naphthoquinone formed the semiquinones of both the monoconjugate and the diconjugate. The naphthoquinone-glutathione conjugates should redox cycle in a manner already known for the menadione conjugate. The semiquinone intermediates could be detected only under a nitrogen atmosphere and are probably the primary oxygen-reactive species responsible for the redox cycling of menadione- and naphthoquinone-glutathione conjugates.
mesh_terms: D016227:Benzoquinones; D004578:Electron Spin Resonance Spectroscopy; D005978:Glutathione / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D009285:Naphthoquinones / Q000378:metabolism; D010084:Oxidation-Reduction; D011809:Quinones / Q000378:metabolism*; D014812:Vitamin K / Q000378:metabolism
chemical_list: D016227:Benzoquinones; D009285:Naphthoquinones; D011809:Quinones; D014812:Vitamin K; C025232:semiquinone radicals; D009249:NADP; D005978:Glutathione; C035342:1,4-naphthoquinone