The mode of action of lipid-soluble antioxidants in biological membranes. Relationship between the effects of ubiquinol and vitamin E as inhibitors of lipid peroxidation in submitochondrial particles.

The effects of ubiquinol and vitamin E on ascorbate- and ADP-Fe(3+)-induced lipid peroxidation were investigated in beef heart submitochondrial particles before and after extraction of ubiquinone and vitamin E, and after reincorporation of either or both of these components. It is concluded that ubiquinol is capable of inhibiting lipid peroxidation without the mediation of vitamin E, but may also amplify the antioxidant effect of the latter. It is pointed out that ubiquinol is the only known lipid-soluble antioxidant that can be synthesized de novo in animal cells, and for which there exists an enzymic mechanism--the mitochondrial electron-transport system--that can regenerate the antioxidant from its oxidized form resulting from its inhibitory effect on lipid peroxidation. These features, together with its high degree of hydrophobicity and its general occurrence in biological membrane and in low-density lipoprotein, suggest a highly important role of ubiquinol in cellular defense against oxidative damage.