Tsuda M, Shikata Y, Katsunuma T
J Biochem. 1979 Mar;85(3):699-704.
The rates of synthesis and degradation of arginosuccinate synthetase in rat liver under various dietary conditions were determined. The relative rate of the enzyme synthesis in the livers of rats fed on 70% casein diet was 4.0 times greater than that for rats fed on 5% casein diet. The rate constants of degradation (Kd of argininosuccinate synthetase were estimated to be 0.15 and 0.16 day-1 under 70% and 5% casein feeding, respectively. When the dietary conditions were changed acutely from 70% to 5% casein diet or vice versa, the rates of the enzyme synthesis decreased or increased, respectively, and the rates of enzyme degradation were also affected. The change from 5% to 70% casein diet caused a transient decrease in the rate of degradation. After the enzyme activity had achieved a new steady-state level, the enzyme degradation proceeded at the normal steady rate. On the other hand, the change from 70% to 5% casein diet caused a transient increase in the rate of degradation. Thus, the only factor regulating the amount of enzyme in rat liver is the rate of enzyme synthesis under the steady-state conditions. However, the rates of both enzyme synthesis and degradation are involved in the regulation of the amount of enzyme during dietary transition.
测定了不同饮食条件下大鼠肝脏中精氨琥珀酸合成酶的合成和降解速率。以70%酪蛋白饮食喂养的大鼠肝脏中该酶的相对合成速率比以5%酪蛋白饮食喂养的大鼠高4.0倍。在70%和5%酪蛋白喂养条件下，精氨琥珀酸合成酶的降解速率常数（Kd）分别估计为0.15和0.16天-1。当饮食条件从70%酪蛋白饮食急性改变为5%酪蛋白饮食或反之亦然时，酶的合成速率分别降低或增加，酶的降解速率也受到影响。从5%到70%酪蛋白饮食的转变导致降解速率短暂下降。当酶活性达到新的稳态水平后，酶的降解以正常的稳态速率进行。另一方面，从70%到5%酪蛋白饮食的转变导致降解速率短暂增加。因此，在稳态条件下，调节大鼠肝脏中酶量的唯一因素是酶的合成速率。然而，在饮食转变过程中，酶的合成和降解速率都参与了酶量的调节。
