Holland R, Witters L A, Hardie D G
Eur J Biochem. 1984 Apr 16;140(2):325-33. doi: 10.1111/j.1432-1033.1984.tb08105.x.
If isolated rat hepatocytes are preincubated for 90 min before addition of hormone, glucagon causes a significant (50%) decrease in fatty acid synthesis without concomitant large decreases in the cellular content of the allosteric activator, citrate. We present evidence that this inhibition can be entirely accounted for by the phosphorylation of the rate-limiting enzyme, acetyl-CoA carboxylase, by cyclic-AMP-dependent protein kinase. In particular: (1) the effect is associated with a 50% decrease in acetyl-CoA carboxylase activity (measured at physiological citrate concentration) which survives purification of the enzyme; (2) the effect is associated with a selective increase in the phosphorylation of a chymotryptic peptide (peptide 1) which is identical to the peptide containing the major site phosphorylated on purified acetyl-CoA carboxylase by cyclic-AMP-dependent protein kinase; (3) the effects of glucagon on the kinetic parameters of the enzyme are very similar to the effect of phosphorylation of the purified enzyme, i.e. a decrease in V and an increase in Ka for citrate; and (4) all of these effects occur at physiological concentrations of glucagon identical to those producing inhibition of fatty acid synthesis.
如果在添加激素之前将分离的大鼠肝细胞预孵育90分钟，胰高血糖素会导致脂肪酸合成显著减少（50%），而变构激活剂柠檬酸的细胞含量不会随之大幅下降。我们提供的证据表明，这种抑制作用完全可以由环磷酸腺苷依赖性蛋白激酶对限速酶乙酰辅酶A羧化酶的磷酸化来解释。具体而言：（1）这种作用与乙酰辅酶A羧化酶活性降低50%有关（在生理柠檬酸浓度下测量），该活性在酶纯化后仍然存在；（2）这种作用与胰凝乳蛋白酶肽段（肽段1）磷酸化的选择性增加有关，该肽段与纯化的乙酰辅酶A羧化酶被环磷酸腺苷依赖性蛋白激酶磷酸化的主要位点所在的肽段相同；（3）胰高血糖素对该酶动力学参数的影响与纯化酶磷酸化的影响非常相似，即V降低，柠檬酸的Ka增加；（4）所有这些作用都发生在与抑制脂肪酸合成相同的生理浓度的胰高血糖素条件下。
