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  • Title: Molecular mechanism of cellular uptake and intracellular translocation of alpha-tocopherol: role of tocopherol-binding proteins.
    Author: Dutta-Roy AK.
    Journal: Food Chem Toxicol; 1999; 37(9-10):967-71. PubMed ID: 10541452.
    Abstract:
    Vitamin E (alpha-tocopherol) is a lipid-soluble antioxidant which is present in cellular membranes where it plays an important role in the suppression of free radical-induced lipid peroxidation. There are eight naturally occurring homologues of vitamin E which differ in their structure and in biological activity in vivo and in vitro. Various studies have suggested that the tocopherol distribution system favours the accumulation of alpha-tocopherol both in the plasma and different tissues. Mechanisms involved in the preferential accumulation of alpha-tocopherol are not yet well established; however, recent data indicate that both intracellular and membrane alpha-tocopherol-binding proteins may be involved in these processes. A 30 kDa alpha-tocopherol-binding protein (TBP) in the liver cytoplasm is now known to regulate plasma vitamin E concentrations by preferentially incorporating alpha-tocopherol into nascent very low density (VLDL) whereas the 15 kDa TBP may be responsible for intracellular distribution of alpha-tocopherol. The 30 kDa TBP is unique to the hepatocyte whereas the 15 kDa TBP is present in all major tissues. The 15 kDa TBP specifically binds alpha-tocopherol in preference to the delta- and gamma-tocopherol and may exclusively transport alpha-tocopherol to these intracellular sites. In addition, the presence of a membrane TBP (TBPpm) in tissues may regulate their alpha-tocopherol levels. Activity of erythrocyte TBPpm appears to be reduced in smokers, which may lead to reduced levels of alpha-tocopherol in these cells despite smokers have similar plasma levels of vitamin E as in non-smokers. The current status of the evidence for this directed flow of alpha-tocopherol through interactions with these proteins (TBP and TBPpm) is discussed.
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