Bosron W F, Crabb D W, Housinger T A, Li T K
Alcohol Clin Exp Res. 1984 Mar-Apr;8(2):196-200. doi: 10.1111/j.1530-0277.1984.tb05837.x.
Alcohol dehydrogenase activity in rat liver decreased with fasting to about 60% of the fed level, but the specific activities of the enzyme purified from livers of fed and 12- or 48-hr fasted animals were similar, 3.2-3.4 U/mg protein. Therefore, the decrease in enzyme activity with fasting should have resulted from a decrease in the amount of enzyme protein. Accordingly, the turnover of alcohol dehydrogenase was examined in fed and fasted rats. The fractional rate of enzyme synthesis (ks) in fed rats was determined by radioisotopic methods to be 0.13 day-1 and it increased to 0.18 day-1 after a 12- or 48-hr fast. The absolute rate of synthesis (V) and the fractional rate of degradation (kd) were calculated from these ks values and the total enzyme content in livers from animals that were fasted for 8 to 72 hr. After 48-72 hr of fasting, V decreased 16% and kd increased about 20% with respect to the fed values. Together, these changes accounted for the lowered enzyme activity in the fasted state. The rapid decrease in enzyme activity with fasting, t1/2 congruent to 16 hr, was found to be due to a rapid increase in kd from 0.14-0.16 day-1 in fed animals to 0.61 day-1 during the first 8 hr after the initiation of fast. Thereafter, kd decreased steadily to reach 0.18 day-1 after 48-72 hr of fasting.
大鼠肝脏中的乙醇脱氢酶活性在禁食时降至进食状态水平的约60%，但从进食动物以及禁食12或48小时动物的肝脏中纯化得到的该酶的比活性相似，为3.2 - 3.4 U/mg蛋白质。因此，禁食时酶活性的降低应是由于酶蛋白量的减少所致。相应地，对进食和禁食大鼠的乙醇脱氢酶周转情况进行了研究。通过放射性同位素方法测定，进食大鼠中酶合成的分数速率（ks）为0.13天⁻¹，禁食12或48小时后增加至0.18天⁻¹。根据这些ks值以及禁食8至72小时动物肝脏中的总酶含量，计算出合成的绝对速率（V）和降解的分数速率（kd）。禁食48 - 72小时后，相对于进食状态的值，V降低了16%，kd增加了约20%。这些变化共同导致了禁食状态下酶活性的降低。发现禁食时酶活性的快速下降（t1/2约为16小时）是由于kd从进食动物的0.14 - 0.16天⁻¹在禁食开始后的前8小时迅速增加至0.61天⁻¹。此后，kd稳步下降，在禁食48 - 72小时后降至0.18天⁻¹。
