ASSAY OF UBIQUINONES AND UBIQUINOLS AS ANTIOXIDANTS

Publisher Summary A diverse range of biological electron-transfer membranes are known to contain a complement of ubiquinones that can undergo redox changes. In membranes of animals, the role of ubiquinones in electron transport is unclear with the notable exception of ubiquinones in mitochondria. In mitochondria, ubiquinones act as mobile distributors of reducing equivalents among the NADH dehydrogenase, succinate dehydrogenase, and cytochrome b–c 1 segment of the electron transport chain and as participants of the protonmotive Q cycle. Ubiquinones are stoichiometrically in excess of electron-transfer chains, additionally, ubiquinones in their reduced form, ubiquinols, may act as free radical scavengers. In chemical systems, vitamin E (α-tocopherol) has a higher reactivity toward peroxyl radicals than ubiquinols. The ubiquinone/ubiquinol redox couple may act efficiently as a mediator in the regeneration of vitamin E by electron transport in cellular membranes. Ubiquinols may be necessary for reducing the vitamin E phenoxyl radical to prevent prooxidant effects of vitamin E in low density lipoproteins (LDL).