Studies of the biological function of vitamin E. II. The nature of the specific activating effect of tocopherol in aged preparations of cytochrome reductases.

Recent work has indicated that evidence supporting a role for tocopherol in electron transport should be re-evaluated. The direct demonstration of the inhibitory nature of solvents on enzymes of the respiratory chain (1) and nonspecific restoration of this activity by various lipids (2, 3) are the major objections to studies which employed isooctane extraction. However, other evidence based on the specific activating effect of tocopherol on aged preparations of cytochrome reductases does suggest a role for tocopherol in the respiratory chain. Thus Nason and Lehman (4), Donaldson et al. (2), and Vasington et al. (5) have shown that under certain conditions of aging, with or without isooctane extraction, some enzyme preparations are activated by the addition of tocopherol. Tocopheryl acetate, tocopherylquinone, and other lipids which reversed the solvent-inhibited enzyme systems were not active in these aged preparations. On the other hand, experiments in which tissues from tocopheroldeficient animals were employed do not support the postulate that tocopherol is involved in electron transport. Thus Corwin and Schwarz (6) have reported unaltered reduced diphosphopyridine nucleotide-cytochrome c reductase activity of liver mitochondria and microsomes obtained from vitamin E-deficient rats. The succinate-cytochrome c reductase activity of these livers from vitamin E-deficient rats was reported to be elevated (7). It has also been reported (8) that the DPNH-cytochrome c reductase activity of a particulate fraction from hearts of vitamin E-deficient chicks was unaltered even though no trace of the vitamin could be demonstrated in whole tissues or enzyme fractions. In the present report, data are presented which are consistent with the view that (a) inhibitory products arise in aged enzyme preparations, and (5) that tocopherol and other hydroxylated compounds reactivate these preparations by removing the inhibitory products. We have examined the specific activating effect of tocopherol on some aged preparations of chick heart muscle.