Tolkovsky A M, Levitzki A
Biochemistry. 1978 Sep 5;17(18):3811-7. doi: 10.1021/bi00611a021.
A detailed kinetic analysis on the rate of activation of adenylate cyclase by 1-epinephrine and by adenosine, separately and combined, was performed. Both ligands were found to induce the activation of adenylate cyclase to its permanently active state in the presence of guanylyl imidodiphosphate (GppNHp). The activation followed strictly first-order kinetics. On the basis of these experiments, it was found that all of the enzyme pool can be activated by the beta-adrenergic receptor, but only 60 to 70% of the enzyme can also be activated by an adenosine receptor. The remaining 30 to 40% cannot be activated by adenosine. While previous experiments have led us to conclude that the epinephrine receptor is uncoupled from the adenylate cyclase, it seems that the adenosine receptor is either precoupled to the enzyme or forms a long-lived intermediate of adenosing-receptor-enzyme complex. From the pattern of enzyme activation by the two ligands and GppNHp, it may be concluded that the two ligands, adenosine and the beta-agonist, activate the adenylate cyclase through a common guanyl nucleotide regulatory site. This assertion is supported by the finding that both adenosine and 1-epinephrine, in the presence of GTP, induce the reversal of the permanently active state, irrespective by which pathway the enzyme was activated.
分别对1-肾上腺素和腺苷单独及联合作用下激活腺苷酸环化酶的速率进行了详细的动力学分析。在鸟苷酰亚胺二磷酸（GppNHp）存在的情况下，发现这两种配体均可诱导腺苷酸环化酶激活至其永久活性状态。激活严格遵循一级动力学。基于这些实验，发现所有的酶库均可被β-肾上腺素能受体激活，但只有60%至70%的酶也可被腺苷受体激活。其余30%至40%不能被腺苷激活。虽然先前的实验使我们得出肾上腺素受体与腺苷酸环化酶解偶联的结论，但似乎腺苷受体要么预先与该酶偶联，要么形成腺苷受体-酶复合物的长寿命中间体。从两种配体和GppNHp对酶的激活模式可以得出结论，腺苷和β-激动剂这两种配体通过一个共同的鸟苷酸调节位点激活腺苷酸环化酶。这一论断得到以下发现的支持：在GTP存在的情况下，腺苷和1-肾上腺素均可诱导永久活性状态的逆转，而无论该酶是通过何种途径被激活的。
