Goodwin C D, Margolis S
J Lipid Res. 1978 Aug;19(6):747-56.
We previously showed that preincubation of a 10,000 g supernatant (S(10)) from rat liver for 20 min at 37 degrees C dramatically increased the subsequent incorporation of [(14)C]acetate into sterols. No activation was seen with [(14)C]mevalonate as substrate. In the present studies we have examined the effect of preincubation on HMG CoA reductase. When microsomes were isolated from S(10) by calcium precipitation, preincubation of S(10) increased the specific activity of HMG CoA reductase threefold. No activation of HMG CoA reductase was observed in microsomes isolated by ultracentrifugation. Activation was cyclic AMP-sensitive. When cyclic AMP (0.001-1.0 mM) and MgATP (1 mM) were present during the preincubation period, there was little or no activation of HMG CoA reductase activity or of sterol synthesis from acetate. MgATP alone did not prevent activation. Neither cyclic AMP nor MgATP was inhibitory when present only during the assay of sterol synthesis. We propose that the in vitro activation represents the reversal of a physiologic cyclic AMP-mediated mechanism for the control of hepatic HMG CoA reductase. That a phosphoprotein phosphatase may catalyze the activation was supported by the observation that sodium fluoride, an inhibitor of phosphoprotein phosphatases, inhibited the activation. These results suggest that hormone-induced changes in the cellular level of cyclic AMP may regulate the activity of HMG CoA reductase and the rate of hepatic cholesterol synthesis.
我们之前发现，将大鼠肝脏的10,000 g上清液（S(10)）在37℃预孵育20分钟，会显著增加随后[(14)C]乙酸盐掺入甾醇的量。以[(14)C]甲羟戊酸为底物时未观察到激活作用。在本研究中，我们检测了预孵育对HMG CoA还原酶的影响。当通过钙沉淀从S(10)中分离微粒体时，S(10)的预孵育使HMG CoA还原酶的比活性提高了三倍。通过超速离心分离的微粒体中未观察到HMG CoA还原酶的激活。激活作用对环磷酸腺苷（cAMP）敏感。当在预孵育期间存在cAMP（0.001 - 1.0 mM）和MgATP（1 mM）时，HMG CoA还原酶活性或乙酸盐合成甾醇的过程几乎没有激活。单独的MgATP并不能阻止激活。仅在甾醇合成测定期间存在时，cAMP和MgATP均无抑制作用。我们提出，体外激活代表了一种生理性的、由cAMP介导的控制肝脏HMG CoA还原酶机制的逆转。磷酸蛋白磷酸酶可能催化激活这一观点得到了以下观察结果的支持：磷酸蛋白磷酸酶抑制剂氟化钠抑制了激活作用。这些结果表明，激素诱导的细胞内cAMP水平变化可能调节HMG CoA还原酶的活性以及肝脏胆固醇合成的速率。
