Vitamin E is the most important lipid-soluble antioxidant in humans. Vitamin E occurs in nature in eight different forms: α-, β-, γ-, δ-tocopherols and -tocotrienols. Although we intake daily diets containing these vitamin E isoforms, our bodies are enriched with only α-tocopherol. This biological discrimination occurs not at the stage of absorption in the intestine but at the stage of secretion from the liver. We isolated a cytosolic protein that specifically binds α-tocopherol and transfers it between separate membranes, and named it α-tocopherol transfer protein (α-TTP). Moreover, we demonstrated that the α-TTP gene is mutated in the patients with familial vitamin E deficiency. To date, about 20 different mutations were identified from the genes of the patients. α-TTP knockout mice were also established and served as a good model for human patients with familial vitamin E deficiency. More attention has been paid to the biological importance of vitamin-E through the studies with vitamin E-deficient patients and mice.
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