VARIATION OF THE ENZYMES OF THE UREA CYCLE AND ASPARTATE TRANSCARBAMYLASE IN LIVER OF PREGNANT RATS

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Abstract
The variations in the specific activities of the enzymes of the urea cycle were studied in the livers of pregnant rats and also in the livers of male rats and other females with the same body weight. The specific activities of the five enzymes of the urea cycle are the same in male and in female except for argininosuccinase. The activity of this enzyme is twice as high in female rats as in male rats. In pregnancy, the activities of the enzymes of the urea cycle are decreased except for arginase, which increases. Aspartate transcarbamylase remains constant during the same period.These results lead to the supposition that another pathway for the synthesis of orotic acid may exist, or more probably that there exist two carbamyl phosphate synthetases, one for pyrimidine biosynthesis and one for urea synthesis.