Is a relay mechanism of antioxidant effect of tocopherols valuable for membrane systems?

The efficiency of the inhibitory action of 3 tocols derivatives--alpha-tocopherol (alpha-T), 2, 2, 5, 7, 8-pentamethylchromane (PMC) and alpha-tocopherylacetate (alpha-TA) on lipid peroxidation (LPO) in rat liver microsomes was compared. LPO was induced by O2-generating systems (Fe2+ + NADPH, Fe2+ + ascorbate) or by ROO generating system (Fe2+ + tert-butyl hydroperoxide). It was found that PMC was much more potent LPO inhibitor than alpha-T, whereas alpha-TA was ineffective in all LPO-initiating systems used. The protective effect against cytochrome P-450 (cyt. P-450) degradation induced by LPO-products was also maximal for PMC and minimal for alpha-TA. The data obtained suggest that the presence of phytyl radical is not necessary for antioxidant activity of tocols and contradict the hypothesis about a relay mechanism of antioxidant action of tocopherols in biomembranes.