Characterization and solubilization of the specific binding sites for d-alpha-tocopherol from human erythrocyte membranes.

Previous work from our laboratory has demonstrated the presence of specific binding sites for d-alpha-tocopherol (vitamin E) in intact human erythrocytes [A. E. Kitabchi and J. Wimalasena, Biochim. biophys. Acta 684, 300 (1982)]. The binding was time, temperature and cell concentration dependent. To localize the binding sites, red blood cells were further fractionated; greater than 90% of the tocopherol binding sites were localized on membranes. The washed membrane fraction from normal human erythrocytes has specific binding sites for d-alpha-tocopherol with properties suggestive of protein receptors. Two binding sites with Ka values of 3.31 x 10(1)M-1 and 1.51 x 10(6)M-1 were demonstrated, and solubilized d-alpha-tocopherol binding site complexes were resolved to a major component with an Mr of 65,000 and a minor component with an Mr of 125,000.