Villar-Palasi C
Department of Pharmacology, Medical School University of Virginia, Charlottesville 22908.
Biochim Biophys Acta. 1994 Jul 20;1207(1):88-92. doi: 10.1016/0167-4838(94)90055-8.
Cyclic AMP-dependent protein kinase phosphorylates and inactivates glycogen synthase. In the absence of cyclic AMP, glycogen synthase is able to partially activate cyclic AMP-dependent protein kinase, probably by inducing the dissociation of the catalytic and regulatory subunits. The activation of cyclic AMP-dependent protein kinase by glycogen synthase is greatly reduced by the addition of low, physiological concentrations of the allosteric activator of glycogen synthase, glucose 6-phosphate. This effect appears to be specific for both glycogen synthase as substrate of the kinase and for cyclic AMP-dependent protein kinase as glycogen synthase phosphorylating enzyme. The result is an apparent, although not real effect of glucose 6-phosphate as an inhibitor competing with cyclic AMP. The reported inhibition by insulin of the activity of cyclic AMP-dependent protein kinase in skeletal muscle may be explained by the increased intracellular levels of glucose 6-phosphate resulting from the action of the hormone on glucose transport.
环磷酸腺苷（cAMP）依赖性蛋白激酶使糖原合酶磷酸化并使其失活。在没有环磷酸腺苷的情况下，糖原合酶能够部分激活环磷酸腺苷依赖性蛋白激酶，可能是通过诱导催化亚基和调节亚基的解离。糖原合酶对环磷酸腺苷依赖性蛋白激酶的激活作用在添加低浓度、生理浓度的糖原合酶变构激活剂6-磷酸葡萄糖后会大大降低。这种效应似乎对作为激酶底物的糖原合酶以及作为使糖原合酶磷酸化的酶的环磷酸腺苷依赖性蛋白激酶都具有特异性。结果是6-磷酸葡萄糖作为与环磷酸腺苷竞争的抑制剂产生了一种明显但并非真实的效应。胰岛素对骨骼肌中环磷酸腺苷依赖性蛋白激酶活性的抑制作用可能是由于该激素对葡萄糖转运的作用导致细胞内6-磷酸葡萄糖水平升高所致。
