Vitamin E Is the Major Lipid Soluble Antioxidant in Cell Membranes Plasma Lipoproteins

The main function of vitamin E is as a chain-breaking, free radical trapping antioxidant in cell membranes and plasma lipoproteins. It reacts with the lipid peroxide radicals formed by peroxidation of polyun-saturated fatty acids before they can establish a chain reaction. The tocopheroxyl free radical product is relatively unreactive and ultimately forms nonradical compounds. Commonly, the tocopheroxyl radical is

Figure 45-5. The vitamin E vitamers. In a-tocoph-erol and tocotrienol R1, R2, and R3 are all —CH3 groups. In the p-vitamers R2 is H; in the y-vitamers R1 is H, and in the 8-vitamers R1 and R2 are both H.

Tocopherol

Tocopherol

Figure 45-5. The vitamin E vitamers. In a-tocoph-erol and tocotrienol R1, R2, and R3 are all —CH3 groups. In the p-vitamers R2 is H; in the y-vitamers R1 is H, and in the 8-vitamers R1 and R2 are both H.

reduced back to tocopherol by reaction with vitamin C from plasma (Figure 45-6). The resultant monode-hydroascorbate free radical then undergoes enzymic or nonenzymic reaction to yield ascorbate and dehy-droascorbate, neither of which is a free radical. The stability of the tocopheroxyl free radical means that it can penetrate farther into cells and, potentially, propagate a chain reaction. Therefore, vitamin E may, like other antioxidants, also have pro-oxidant actions, especially at high concentrations. This may explain why, although studies have shown an association between high blood concentrations of vitamin E and a lower incidence of atherosclerosis, the effect of high doses of vitamin E have been disappointing.

Diabetes 2

Diabetes 2

Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...

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