Evans P J
Biochim Biophys Acta. 1981 Nov 5;677(3-4):433-44. doi: 10.1016/0304-4165(81)90257-9.
Tyrosine aminotransferase induction has been studied in hepatocytes from untreated, partially and fully glucocorticoid-induced rats: enzyme activities were initially 12.9 +/- 1.7 (n = 16), 41.4 +/- 3.2 (n = 6) and 117.9 +/- 10.5 (n = 7) munits/mg protein, respectively. Untreated or fully induced hepatocytes maintain initial levels, whereas partially induced hepatocytes increase their tyrosine aminotransferase activity even in the presence of actinomycin D. Fully induced hepatocytes possess a normal protein synthetizing machinery and the mechanisms to degrade selectively tyrosine aminotransferase. The effect of progesterone treatment is consistent with these cells retaining a high dexamethasone level. Glucagon induces tyrosine aminotransferase via its second messenger, cyclic AMP. This induction decreases dramatically with in vivo glucocorticoid treatment. Time courses and effects of inhibitors are consistent with these in vivo and in vitro treatments being alternative methods of inducing tyrosine aminotransferase by the same basic pretranslational step.
已对未处理、部分糖皮质激素诱导和完全糖皮质激素诱导的大鼠肝细胞中的酪氨酸转氨酶诱导情况进行了研究：酶活性最初分别为12.9±1.7（n = 16）、41.4±3.2（n = 6）和117.9±10.5（n = 7）微单位/毫克蛋白质。未处理或完全诱导的肝细胞维持初始水平，而部分诱导的肝细胞即使在放线菌素D存在的情况下也会增加其酪氨酸转氨酶活性。完全诱导的肝细胞拥有正常的蛋白质合成机制以及选择性降解酪氨酸转氨酶的机制。孕酮处理的效果与这些细胞保留高浓度地塞米松一致。胰高血糖素通过其第二信使环磷酸腺苷诱导酪氨酸转氨酶。这种诱导在体内糖皮质激素处理后显著降低。抑制剂的时间进程和作用与这些体内和体外处理是通过相同的基本翻译前步骤诱导酪氨酸转氨酶的替代方法一致。
