| Abstrakt: |
Although it has been reported that α-tocopherol acts as a lipid antioxidant, that it inhibits various enzymes involved in biological oxidation, and that α-tocopherol stabilizes the cell membrane, the exact function of the vitamin in the cell membrane is still unknown. Using partially and highly purified Na,K-ATPase preparations, the effects of tocopherols and their derivatives were tested as sonicated suspensions in water. α-Tocopherol and α-tocopherylquinone inhibited the Na,K-ATPase with one-half maximal inhibition at 5.7 × 10-5M and 3.1 × 10-5M, respectively (near the physiological vitamin E concentration in blood, 3 × 10-5M). Other tocopherol derivatives and fat-soluble vitamins did not show such strong inhibition. For example, the Ki value of a-tocopheryl acetate was 50 times greater than that of free cs-tocopherol. BHT, cysteine, and DTT did not affect the inhibition. Ca ATPase from muscle was similarly inhibited. On the other hand, ouabain-insensitive ATPase from rabbit brain and liver was slightly affected. There seemed to be no effect on acetylcholinesterase from human erythrocytes, and little or no effect on 5-nucleotidase and G6Pase from rabbit brain. Some kinetical examination of α-tocopherol and α-tocopherylquinone was performed. [ABSTRACT FROM AUTHOR] |
