Tolkovsky A M, Braun S, Levitzki A
Proc Natl Acad Sci U S A. 1982 Jan;79(2):213-7. doi: 10.1073/pnas.79.2.213.
The kinetics of turkey erythrocyte membrane adenylate cyclase activation by beta-agonists and guanyl-5'-yl imidodiphosphate is explored as a function of the concentration of the GTP regulatory protein and of the catalytic unit. It was found that the overall kinetics of activation is first order and is independent of the concentration of the GTP regulatory unit N, the catalytic unit C, and of hormone over a very wide concentration range. It was established that the rate-limiting step does not involve GDP dissociation from the inactive N unit or the association between activated N' and C. Also, it was found that guanyl-5'-yl imidodiphosphate binding occurs in a random fashion and is not hormone dependent. These results enable us to exclude models of the sequential type in which N in its inactive form is bound to receptor R, is released in an active form N' upon hormone activation, and then binds to C, activating the latter. An acceptable model that accounts for all of the data conforms to the original formulation of "collision coupling" in which N is tightly associated to C at all times.
研究了β-激动剂和鸟苷-5'-基亚氨基二磷酸对火鸡红细胞膜腺苷酸环化酶的激活动力学，该动力学是GTP调节蛋白和催化单位浓度的函数。研究发现，激活的总体动力学是一级的，并且在非常宽的浓度范围内与GTP调节单位N、催化单位C和激素的浓度无关。已确定限速步骤不涉及GDP从无活性的N单位解离或活化的N'与C之间的结合。此外，还发现鸟苷-5'-基亚氨基二磷酸的结合是随机发生的，且不依赖于激素。这些结果使我们能够排除顺序型模型，在该模型中，无活性形式的N与受体R结合，在激素激活后以活性形式N'释放，然后与C结合，激活后者。一个能解释所有数据的可接受模型符合“碰撞偶联”的原始表述，即N在任何时候都与C紧密结合。
