抄録
1) Nitrogen sparing effect of dietary fat
The present study was carried out to investigate whether the nitrogen sparing effect of carbohydrate and fat is correlated with the activities of some amino acid-catabolizing enzymes: threonine dehydratase, tryptophan pyrrolase and arginase. Dietary fat depressed exogenous and also endogenous nitrogen output in urine. Furthermore, switchover from a high carbohydrate diet to a high fat diet led to an increase in the nitrogen output, while switchover from a high fat diet to a high carbohydrate diet led to a reduction in the nitrogen output. In these four cases, it was found that there was correlation between the nitrogen output in urine and the activities of amino acid-catabolizing enzymes mentioned above. Thus, it may be concluded that the nitrogen output is regulated by the activities of liver amino acidcatabolizing enzymes under these conditions.
2) Metabolic specificity of lysine and threonine
The amount of free threonine in liver and muscle was greatly increased by feeding of a threonine-excess diet, while decreased by that of a threonine-deficient diet. In contrast, the free lysine level did not undergo any significant alteration by feeding of a lysine-excess or a lysine-deficient diet. Decomposition to respiratory carbon dioxide and conversion to carbohydrates and lipids from threonine was not much affected by the changes in the amount of threonine in diets. Meanwhile, these decomposition and conversion from lysine was greatly altered by excess or deficiency of lysine in diets. From these experiments, it is supposed that lysine is more easily controlled homeostatistically than threonine.
