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-Fe3+-induced lipid peroxidation were investigated by measuring oxygen consumption and malondialdehyde formation in beef heart submitochondrial particles. In the native particles, lipid peroxidation showed an initial lag phase, which was prolonged by increasing concentrations of ascorbate. Lipid peroxidation in these particles was almost completely inhibited by conditions leading to a reduction of endogenous ubiquinone, such as the addition of succinate or NADH in the presence of antimycin. Lyophilization of the particles followed by three or four consecutive extractions with pentane resulted in a complete removal of vitamin E and a virtually complete removal of ubiquinone, as revealed by reversed-phase high pressure liquid chromatography. In these particles, lipid peroxidation showed no significant lag phase and was not inhibited by either increasing concentrations of ascorbate or conditions leading to ubiquinone reduction. Treatment of the particles with a pentane solution of vitamin E (alpha-tocopherol) restored the lag phase and its prolongation by increasing ascorbate concentrations. Treatment of the extracted particles with pentane containing ubiquinone-10 resulted in a restoration of the inhibition of lipid peroxidation by succinate or NADH in the presence of antimycin, but not the initial lag phase or its prolongation by increasing concentrations of ascorbate. Malonate and rotenone, which prevent the reduction of ubiquinone by succinate and NADH, respectively, abolished, as expected, the inhibition of the initiation of lipid peroxidation in both native and ubiquinone-10-supplemented particles. Reincorporation of both vitamin E and ubiquinone-10 restored both effects.(ABSTRACT TRUNCATED AT 250 WORDS)