Wallace R W, Lynch T J, Tallant E A, Cheung W Y
J Biol Chem. 1979 Jan 25;254(2):377-82.
A heat-labile inhibitor protein of adenylate cyclase (EC 4.6.1.1) and phosphodiesterase (EC 3.1.4.17) has been purified to apparent homogeneity from bovine brain cerebrum by a simple two-column procedure. The inhibitor exerts its effect on adenylate cyclase or phosphodiesterase by forming a complex with the Ca2+-dependent activator protein, thereby competing with the apoenzyme for the activator. The protein was estimated to have a molecular weight of 80,000 and a Stokes radius of 39 A by gel filtration. The inhibitor was resolved in a sodium dodecyl sulfate-polyacrylamide gel into two equal molar subunits, with molecular weights of 60,000 and 18,500. In the presence of the activator and Ca2+, the thermal stability of the inhibitor was increased, indicative of a new conformation. The effectiveness of the inhibitor varied considerably, depending on its sequence of addition to the reaction mixture relative to phosphodiesterase and the activator protein, presumably because the activator appeared to have a greater affinity for the inhibitor than for phosphodiesterase.
一种对腺苷酸环化酶（EC 4.6.1.1）和磷酸二酯酶（EC 3.1.4.17）具有热不稳定作用的抑制蛋白，已通过一种简单的双柱法从牛脑大脑中纯化至表观均一状态。该抑制剂通过与钙依赖性激活蛋白形成复合物，从而与脱辅基酶竞争激活剂，进而对腺苷酸环化酶或磷酸二酯酶发挥作用。通过凝胶过滤估计该蛋白的分子量为80,000，斯托克斯半径为39埃。该抑制剂在十二烷基硫酸钠 - 聚丙烯酰胺凝胶中分解为两个等摩尔亚基，分子量分别为60,000和18,500。在激活剂和钙离子存在的情况下，抑制剂的热稳定性增加，表明形成了一种新的构象。抑制剂的有效性差异很大，这取决于其相对于磷酸二酯酶和激活蛋白添加到反应混合物中的顺序，推测是因为激活剂对抑制剂的亲和力似乎比对磷酸二酯酶的亲和力更大。
