Goodridge A G, Adelman T G
J Biol Chem. 1976 May 25;251(10):3027-32.
Cells isolated from the livers of 17- to 19-day-old chick embryos were maintained in a chemically defined culture medium. During 3 days in culture the activity of malic enzyme, a measure of its concentration, was stimulated 2-, 23-, or 77-fold by insulin, triiodothyronine, or insulin plus triiodothyronine, respectively. Glucagon blocked the stimulation caused by insulin plus triiodothyronine. Changes in the relative synthesis of immunologically isolated malic enzyme were similar in magnitude and direction to the changes in enzyme activity. Degradation of malic enzyme was unaffected by the three hormones. Both soluble protein and malic enzyme were degraded with a t1/2 of about 30 hours. In cells preincubated for 2 days with insulin, synthesis of malic enzyme was stimulated 4.5-fold within 3 hours after adding triiodothyronine and reached an apparent new steady state after 24 to 30 hours. If the rate of enzyme synthesis was dependent on the concentration of cytoplasmic malic enzyme messenger RNA, then this messenger RNA appeared to have a t1/2 of about 18 hours. Glucagon rapidly and specifically inhibited synthesis of malic enzyme in preinduced cells, suggesting an action at the level of translation or cytoplasmic messenger RNA processing.
从17至19日龄鸡胚肝脏分离出的细胞，在化学成分明确的培养基中培养。在培养的3天里，苹果酸酶的活性（衡量其浓度的指标）分别被胰岛素、三碘甲状腺原氨酸或胰岛素加三碘甲状腺原氨酸刺激了2倍、23倍或77倍。胰高血糖素阻断了胰岛素加三碘甲状腺原氨酸所引起的刺激。免疫分离的苹果酸酶相对合成的变化在幅度和方向上与酶活性的变化相似。三种激素均未影响苹果酸酶的降解。可溶性蛋白质和苹果酸酶均以约30小时的半衰期降解。在用胰岛素预孵育2天的细胞中，加入三碘甲状腺原氨酸后3小时内，苹果酸酶的合成被刺激了4.5倍，并在24至30小时后达到明显的新稳态。如果酶合成速率取决于细胞质苹果酸酶信使核糖核酸的浓度，那么这种信使核糖核酸的半衰期似乎约为18小时。胰高血糖素迅速且特异性地抑制预诱导细胞中苹果酸酶的合成，表明其作用于翻译或细胞质信使核糖核酸加工水平。
