Vitamin E Deficiency in the Rat

Experiments were conducted to determine which of the required factors for β-hydroxybutyrate dehydrogenase activity becomes limiting when vitamin E-deficient liver homogenates or combinations of mitochondria and microsomes from the livers of either vitamin E-deficient or vitamin E-supplemented rats oxidize β-hydroxybutyrate. Nicotinamide adenine dinucleotide was the only one of the required cofactors which was effective in restoring β-hydroxybutyrate oxidation in both vitamin E-deficient homogenates and in all combinations of mitochondria and microsomes. An initial concentration of 3 mm NAD delayed the onset of decline in oxidation by combinations of mitochondria and microsomes beyond that observed with an initial NAD concentration of 1 mm. The delaying effect due to extra NAD was more pronounced in the combination of vitamin E-supplemented mitochondria and microsomes. NADase activity was highest when microsomes of either type were present, although this activity was not always correlated with respiratory decline. However, the addition of nicotinamide, an inhibitor of NADase, prevented the microsomal-induced decline in oxidation. A study of the effect of pH on inhibitory activity revealed enhanced inhibition as the pH was lowered from 7.5 to 6.8. It is suggested that the microsomal inhibitor is the enzyme NADase and that it is mainly responsible for the respiratory decline. However, supernatant factors can prevent respiratory decline when E-supplemented microsomes are present even though the NAD concentration is quite low. An additional effect of E-deficient microsomes, which is closely related to NAD function, is possible.