Identification of a Low Molecular Mass (14.2 kDa) α-Tocopherol-Binding Protein in the Cytosol of Rat Liver and Heart

An α-tocopherol-binding protein (TBP) with a molecular mass of 14.2 kDa has been identified from the cytosol of rat heart and liver and purified to electrophoretic homogeneity by precipitation with 70% ammonium sulphate, followed by gel filtration and ion-exchange chromatography. In addition to the 14.2 kDa TBP, liver also contains the previously described 30 kDa TBP. The concentrations of the 14.2 kDa TBP in heart and liver were 12.3 μg and 17.5 μg per g of tissue, respectively. The purified protein specifically binds dα-tocopherol in preference to the δ- and γ-homologues but does not bind oleate. The TBP stimulated the transfer of dα-tocopherol from liposomes to mitochondria in vitro by 8-10 fold. These results suggest that low molecular mass TBPs may play a role in intracellular vitamin E transport.