栄養素組成と体蛋白質の代謝-2-
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概要
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In this laboratory, we have been attempting to study the dietary requirements from the view point of metabolism, especially of enzyme activities, constituents, and its turnover rates. As previously reported, we have observed that the activities of liver xanthine oxidase and choline oxidase were affected greatly by varying levels of dietary protein in rats. In this paper, we wanted to account for the relation between liver enzyme activities and the nitrogen metabolites in urine by varying levels of dietary protein. The enzymes chosen for the present research were liver xanthine oxidase and arginase which played a role in nucleic acid and protein metabolism, respectively. As the nitrogen metabolites in urine, uric acid, allantoine, xanthine, urea and creatinine were determined. The results are shown in Table 1_??_2 and Fig. 1_??_6. The activity of liver xanthine oxidase was depleted to zero on the free- and low-protein (10%) diet, and maintained constant level on 20_??_30% protein diets as previously indicated, while the activity of liver arginase increased linearly with increasing protein percentage of the ration. On the other hand the excretions of nitrogen metabolites increased according to the amounts of dietary protein, the increasing rate of urea being larger than that of uric acid and allantoin. Even on the protein-free ration, excretion of xanthine in the urine was not observed. The amount of urinary creatinine was found to be unaltered by varying amount of protein, except a little increase on the protein-free ration. The above results demonstrates that there is a close relationship between the activity of liver arginase and the amount of urinary urea, but is no relationship between the activity of liver xanthine oxidase and the urinary excretion of uric acid and allantoin.