Reactions of superoxide ion with redox-active substances of physiological importance: Generation of semiquinone radicals from physiologically important quinones.

Abstract

The reactions of superoxide ion, O2-, with physiologically important quinones were investigated in acetonitrile by electron spin resonance (ESR) spectroscopy. Superoxide ion could reduce quinones such as p-benzoquinone, duroquinone, vitamin E quinone, 1, 4-naphthoquinone and vitamin K3 to yield the corresponding semiquinone radicals. The fact that vitamin E quinone, an irreversible metabolite of vitamin E, was reduced by O2- to the semiquinone radical suggests that, like vitamin E, vitamin E quinone may also scavenge O2- and protect living cells from the effects of O2- in a hydrophobic environment. Further, in view of the apparent reversiblity of the reaction of O2- with vitamin K3, it is unlikely that the in vivo toxicity of vitamin K3 is solely due to O2- production, as has been suggested.