The main role of vitamin E is as an antioxidant to neutralize free radicals in cell membranes, in mitochondrial membranes, and in LDL. The fats in cell membranes are susceptible to oxidation by free radicals. The interior of the cell membrane is inaccessible to water-soluble antioxidants. The fat-soluble tocopherols are perfectly
suited to protecting cell membranes from free radicals. The fat-soluble tail of the tocopherol can reach in and neutralize the free radicals, as seen in Figure 5-3.Vitamin E also protects polyunsaturated fatty acids and vitamin A from free radical damage.
Vitamin E neutralizes free radicals by donating a hydrogen atom from the hydroxyl group (HO) on the hexagonal head of vitamin E, as seen in Figure 5-4. Donation of hydrogen to a free radical is easiest for the alpha-tocopherol and
Figure 5-3 Tocopherol can reach deep inside the cell membrane.
Figure 5-4 Free radical neutralization in a cell membrane with tocopherol.
gamma-tocopherol forms and slightly harder for the beta-tocopherol and deltatocopherol forms. In cell membranes, the hexagonal head of vitamin E stays near the surface of the membrane. The tail of vitamin E is deeply implanted into the cell membrane. When the tail of vitamin E is oxidized by a free radical, it moves to the surface where the head of the vitamin E can donate hydrogen. In this way, vitamin E pulls free radicals out of fatty membranes for neutralization. This vitamin E cannot perform its antioxidant function a second time until it is regenerated.
The ability of vitamin E to perform as an antioxidant can be restored by the ascorbate form of vitamin C or by coenzyme Q. After restoring the antioxidant activity of vitamin E, the vitamin C then needs glutathione to restore its own antioxidant activity, as seen in Figure 5-5. In reactivating these antioxidants, both niacin and lipoic acid may play a role. Vitamin E has the potential to act as a free radical rather than as an antioxidant when co-antioxidants such as vitamin C are not available.
Figure 5-5 Regeneration of vitamin E with vitamin C and glutathione
suited to protecting cell membranes from free radicals. The fat-soluble tail of the tocopherol can reach in and neutralize the free radicals, as seen in Figure 5-3.Vitamin E also protects polyunsaturated fatty acids and vitamin A from free radical damage.
Vitamin E neutralizes free radicals by donating a hydrogen atom from the hydroxyl group (HO) on the hexagonal head of vitamin E, as seen in Figure 5-4. Donation of hydrogen to a free radical is easiest for the alpha-tocopherol and
Figure 5-3 Tocopherol can reach deep inside the cell membrane.
gamma-tocopherol forms and slightly harder for the beta-tocopherol and deltatocopherol forms. In cell membranes, the hexagonal head of vitamin E stays near the surface of the membrane. The tail of vitamin E is deeply implanted into the cell membrane. When the tail of vitamin E is oxidized by a free radical, it moves to the surface where the head of the vitamin E can donate hydrogen. In this way, vitamin E pulls free radicals out of fatty membranes for neutralization. This vitamin E cannot perform its antioxidant function a second time until it is regenerated.
The ability of vitamin E to perform as an antioxidant can be restored by the ascorbate form of vitamin C or by coenzyme Q. After restoring the antioxidant activity of vitamin E, the vitamin C then needs glutathione to restore its own antioxidant activity, as seen in Figure 5-5. In reactivating these antioxidants, both niacin and lipoic acid may play a role. Vitamin E has the potential to act as a free radical rather than as an antioxidant when co-antioxidants such as vitamin C are not available.
Figure 5-5 Regeneration of vitamin E with vitamin C and glutathione
or niacin.
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