CHANGES OF ENZYME ACTIVITIES WITH DIET AND THYROXINE DURING POSTNATAL DEVELOPMENT OF RAT

1. 1. The evolution of α-glycerophosphate oxidase (L-glycerol-3-phosphate: (acceptor) oxidoreductase, EC 1.1.99.5) and malate dehydrogenase (decarboxylating) (NADP) (L-malate:NADP oxidoreductase (decarboxylating), EC 1.1.1.40) activities in the brown adipose tissue of young rats (control and hyperthyroid) is described. Both enzyme activities are greater than in liver and less sensitive to thyroxine. 2. 2. When the animals are fed from weaning with semi-synthetic diets (high in fats or high in carbohydrates) the α-glycerophosphate oxidase activity is the same as it is with laboratory chow. The malate dehydrogenase activity increases during the weaning period with the high-carbohydrate diet, but stays at the suckling level with the high-fat diet. 3. 3. In the liver the α-glycerophosphate oxidase activity fails to decrease after weaning with either semi-synthetic diets. Liver malate dehydrogenase increases more and is more sensitive to thyroxine with the high-carbohydrate diet than with the high-fat diet. 4. 4. The significance of these results is discussed, especially in respect to brown adipose tissue. © 1968.