Effects of diet on HMP dehydrogenase and malic (TPN) dehydrogenase in the rat

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Abstract
The effects of several types of diets and feeding procedures on the activities of hexose monophosphate (HMP) dehydrogenase and malic (TPN) dehydrogenase were studied in rats. Inclusion of dietary fat at levels 15% or above depressed activity of both enzymes. Diets high in protein, and containing only 2% carbohydrate, depressed the activity of malic (TPN) dehydrogenase, but had no effect on HMP shunt dehydrogenase. Fat, fed concurrently with carbohydrate, depressed activity of both enzymes, but had little effect when fed on alternate days. Regeneration of HMP dehydrogenase activity after fasting was greatest during 75% protein + 17% alanine refeeding, followed in intensity by 90% protein, 75% protein + 17% glutamic acid, and least on an N-free high-carbohydrate diet. Malic (TPN) dehydrogenase, under these circumstances, was stimulated only by the N-free high-carbohydrate diet. Substitution of starch or dextrin for glucose in high-carbohydrate diets had a depressing effect on both of the enzymes studied.