Location and recycling of mitochondrial alpha-tocopherol

Vitamin E in the form of alpha-tocopherol is crucial for mitochondrial integrity. We studied the distribution of alpha-tocopherol in rat muscle mitochondria in relation to the capacity of the electron transport chain to recycle the vitamin. Fractionation studies showed that almost 90% of the alpha-tocopherol in mitochondria is located in the outer membrane. This distribution was confirmed with the finding that ferricytochrome c, which does not penetrate the outer membrane, oxidized 70-80% of mitochondrial alpha-tocopherol in a time- and concentration-dependent manner. Despite the predominant outer membrane distribution of alpha-tocopherol, succinate and other mitochondrial respiratory substrates spared alpha-tocopherol from oxidative loss by both agents. Sparing of alpha-tocopherol by succinate was prevented by 2-thenoyltrifluoroacetone, but not by myxothiazol, which suggests that ubiquinol is the electron donor. Ferricytochrome c significantly increased total F2-isoprostanes, an effect that was prevented by succinate. Most alpha-tocopherol in muscle mitochondria is located in the outer membrane, where it is susceptible to oxidative loss. Nonetheless, alpha-tocopherol is partially spared by ubiquinol in the electron transport chain.