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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.Copyright 1993, 1999 Academic Press

When stress-susceptible and stress-resistant pigs consumed diets containing 10 iu vitamin E kg−1, the stress-susceptible pigs had damaged cell membranes. This was indicated by increased plasma activities of creatine kinase and pyruvate kinase. Plasma concentrations of thiobarbituric acid reactive substances and conjugated dienes were also increased suggesting that the membrane damage was caused by free radicals. Susceptibility to free radicals was further demonstrated by an increased tendency for erythrocytes and tissue homogenates from stress-susceptible pigs to peroxidise when incubated with hydrogen peroxide and iron, respectively. Supplementation of the diets with approximately 20 times normal requirements of vitamin E decreased plasma creatine kinase and pyruvate kinase activities, and inhibited the formation of the indices of peroxidation in vivo and in vitro. It is concluded that the stress-susceptible pig has an abnormality in its antioxidant defence mechanisms. However, this abnormality was not due to a deficiency in selenium-dependent glutathione peroxidase, since activities were significantly increased in the longissimus dorsi of stress-susceptible pigs. Although the nature of the antioxidant defect is unclear, it is suggested that stress-susceptible pigs are under a sustained oxidant stress and that a decreased ability to accommodate even a normal free radical load may contribute to the rapid development of the fatal stress response.

We previously reported the identification of a new α-tocopherol-binding protein (∼ 15 kDa) in the cytosol of rat liver and heart and in rabbit heart (A, K, Dutta-Roy et al., J, Nutr, Biochem. 5, 562-570, 1994). This protein specifically binds α-tocopherol and enhances its transfer between separate membranes, In the present paper we have purified and characterized the α-tocopherol-binding protein from bovine heart cytosol and compared its various structural and functional properties with the similar size (∼ 15 kDa) cytosolic fatty acid-binding protein of this tissue. α-Tocopherol-binding protein was purified to electrophoretic homogeneity from bovine heart cytosol by a procedure involving precipitation with 70% ammonium sulfate, followed sequentially by gel filtration chromatography and chromatofocusing, 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 that the pIvalue is around 4.5. The binding of α-tocopherol to the purified protein was rapid, reversible, and saturable. The α-tocopherol-binding protein did not bind oleate as assessed by direct radiolabeled fatty acid binding and fluorescence enhancement assay, Amino acid analysis showed the presence of a large number of Ala, Gly, Ser, Lys, 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 α-tocopherol-binding protein in the Western blot. The Western blot, ligand affinity, molecular size, and amino acid analysis data suggest that the α-tocopherol-binding protein is different from the cytosolic fatty acid-binding protein and that it may be involved in intracellular transport and metabolism of α-tocopherol.

Inflammatory disorders of the bowel and colon cancer are associated with elevated indices of oxidative stress. Analogous elevations in markers of oxidative stress and loss of cell-membrane integrity are also observed in the colons of rats deficient in vitamin E (D-α-tocopherol), the major lipid-soluble antioxidant in biological systems. The causal relationship between colon pathologies associated with oxidative stress and dietary deficiency in antioxidant vitamins such as vitamin E is still uncertain. Investigation of potential mechanisms by which lack of dietary vitamin E may lead to clinically relevant pathological changes in colon tissue was conducted using gene expression profiling strategies on vitamin E-sufficient and -deficient rats. Morphological changes and increased indices of lipid peroxidation were linked to vitamin E deficiency. These changes in colon tissue are potentially important in disease pathogenesis of the colon linked with oxidative stress or other direct consequences of inadequate levels of vitamin E.

The inclusion into single cells of endosymbionts that became mitochondria was crucial in promoting the evolution of life on Earth. This was because the energy to fuel growth and reproduction could now be more efficiently obtained from stepwise reduction of molecular oxygen to water. Under these conditions, however, oxygen is also toxic-a by-product of ATP production by the mitochondrial respiratory chain with leakage of superoxide into the cell. This reactive form can be transformed into other free radical species and non-radical derivatives that can damage biological molecules such as lipids, proteins and DNA. Oxidative damage from both endogenous sources and exogenous sources (e.g. smoking, ionizing radiation, ultraviolet light) is involved in the development of many diseases (Figure 1).