a-Tocopherol transfer protein (aTTP), a product of the gene which causes familial isolated vitamin E deficiency, plays an important role in determining the plasma vitamin E level. We examined the structural characteristics of vitamin E analogs required for recognition by aTTP. Ligand specificity was assessed by evaluating the competition of non-labeled vitamin E analogs and a-[ 3 H|tocopherol for transfer between membranes in vitro. Relative affinities (/J/?/?-a-tocopherol = 100%) calculated from the degree of competition were as follows: ß-tocopherol, 38%; y-tocopherol, 9%; 5-tocopherol, 2%; a-tocopherol acetate, 2%; a-tocopherol quinone, 2%; SRRa-tocopherol, 11%; a-tocotrienol, 12%; trolox, 9%. Interestingly, there was a linear relationship between the relative affinity and the known biological activity obtained from the rat résorption-gestation assay. From these observations, we conclude that the affinity of vitamin E analogs for aTTP is one of the critical determinants of their biological activity. © 1997 Federation of European Biochemical Societies.

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