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Abstract
1. The antioxidant effects of α-tocopherol and α-tocopherol acetate were assayed for the (a) oxygen uptake, (b) chemiluminescence and (c) malondialdehyde formation, of tert-butyl hydroperoxide-supplemented rat liver microsomes.
2. Oxygen uptake was inhibited 60% by both α-tocopherol and α-tocopherol acetate with the half-maximal effect at 5 nmol tocopherol/mg protein. Chemiluminescence and malondialdehyde formation were equally inhibited 35% by both tocopherols with half-maximal effects at 2 nmol tocopherol/mg protein.
3. The rate of O2 uptake by tocopherol-supplemented microsomes was dependent on O2 concentration. A 60% inhibition by 5 nmol tocopherol/mg protein at 0.2 mM O2 is decreased to 5% inhibition at 0.6 mM O2.
4. The inhibition of O2 uptake, chemiluminescence and malondialdehyde formation indicate that both α-tocopherol and α-tocopherol acetate have similar effects as free radical traps in the hydrophobic domain of biomembranes. The different inhibition observed at different O2 concentrations indicate competition between vitamin E and O2 by unoxygenated lipid radicals.