CHARACTERIZATION OF A NOVEL ALPHA-TOCOPHEROL-BINDING PROTEIN FROM BOVINE HEART CYTOSOL

We previously reported the identification of a new alpha-tocopherol-bi nding protein (similar to 15 kDa) in the cytosol of rat liver and hear t and in rabbit heart (A, K, Dutta-Roy et al., J, Nutr, Biochem, 5, 56 2-570, 1994). This protein specifically binds cr-tocopherol and enhanc es its transfer between separate membranes, In the present paper we ha ve purified and characterized the alpha-tocopherol-binding protein fro m bovine heart cytosol and compared its various structural and functio nal properties with the similar size (similar to 15 kDa) cytosolic fat ty acid-binding protein of this tissue, alpha-Tocopherol-binding prote in was purified to electrophoretic homogeneity from bovine heart cytos ol by a procedure involving precipitation with 70% ammonium sulfate, f ollowed sequentially by gel filtration chromatography and chromatofocu sing, The purified protein migrated as a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with an apparent molecular mass of 16 kDa, Isoelectric focusing of the purified protein showed t hat the pI value is around 4.5, The binding of alpha-tocopherol to the purified protein was rapid, reversible, and saturable, The alpha-toco pherol-binding protein did not bind oleate as assessed by direct radio labeled fatty acid binding and fluorescence enhancement assay, Amino a cid analysis showed the presence of a large number of Ala, Gly, Ser, L ys, and Pro residues and a lesser number of aromatic residues in this protein, Anti-bovine heart fatty acid-binding protein antibody did not recognize the alpha-tocopherol-binding protein in the Western blot, T he Western blot, ligand affinity, molecular size, and amino acid analy sis data suggest that the alpha-tocopherol-binding protein is differen t from the cytosolic fatty acid-binding protein and that it may be inv olved in intracellular transport and metabolism of alpha-tocopherol. ( C) 1995 Academic Press,Inc.