Tocopherol-binding protein

StockerAandAzziA (2000) Tocopherol-binding proteins their function and physiological significance. Antioxidants and Redox Signaling 2,397-404. 

The bioactivity of E-vitamers is defined as their ability to prevent or reverse specific vitamin E deficiency symptoms, such as fetal resorption in rats and muscular dystrophy and encephalomalacia in chicken (Machlin, 1991). The bioactivities of different E-vitamers parallel their bioavailability, indicating that bioactivity is more a function of the amounts available in the body than the chemical activities of these vitamers. Because diets are reasonably abundant in E-vitamers, vitamin E deficiency is rare in humans and is almost limited to malnourished people, people with fat malabsorption or those with a defect in the hepatic tocopherol binding protein (Dutta-Roy et al., 1994). 

Dutta-Roy, A.K., Gordon, M.J., Campbell, F.M., Duthie, G.G., and James, W.P. 1994. Vitamin E Requirements, Transport and Metabolism Role of CX-Tocopherol Binding Proteins. J. Nutr. Biochem. 5 562-570. 

In the last decade, several proteins have been described that can bind tocopherols, however, their role in intracellular distribution of the tocopherols remains to be shown in detail." A 14.2 kDa tocopherol-binding protein (TBP) was shown to enhance up to ten-fold the transport of a-tocopherol to the mitochondria.Among the tocopherol-binding proteins, only a-TTP and several human tocopherol associated proteins (hTAPl, hTAP2, hTAP3) have been cloned and shown in vitro to bind tocopherol with reasonable affinity (Table 12.1). -" ... 

Catignani, G.L., An alpha-tocopherol binding protein in rat liver cytoplasm, Biochem. Biophys. Res. Commun. 67 (1), 66-72., 1975. 

Dutta-Roy, A.K., Alpha-tocopherol-binding proteins purification and characterization, Methods Enzymol. 282, 278-297, 1997. 

Dutta-Roy, A.K., Molecular mechanism of cellular uptake and intracellular translocation of alpha-tocopherol role of tocopherol-binding proteins. Food. Chem. Toxicol. 

There are two mechanisms for tissue uptake of vitamin E. Lipoprotein lipase releases the vitamin by hydrolysing the triacylglycerols in chylomicrons and VLDL, while separately there is uptake of LDL-bound vitamin E by means of LDL receptors. Retention within tissues depends on binding proteins, and it is likely that the differences in biological activity of the vitamers are due to differential protein binding. y-Tocopherol and a-tocotrienol bind relatively poorly, whereas 5 i i -a-tocopherol and RRR-a-tocopherol acetate do not bind to liver tocopherol-binding protein to any significant extent. 

Kuhlenkamp, 1, Ronk, M, Yusin, M, Stolz, A and Kaplowitz, N (1993) Identification and purification of a human liver cytosolic tocopherol binding protein. Prot. Express. Purific.,... 

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