Kreiner P W, Keirns J J, Bitensky M W
Proc Natl Acad Sci U S A. 1973 Jun;70(6):1785-9. doi: 10.1073/pnas.70.6.1785.
We describe an abrupt increase (at 32 degrees ) in the energy of activation for the reaction of hepatic adenylyl cyclase in the presence of glucagon or epinephrine. This increase is not seen in the presence of fluoride, prostaglandin E(1), or 1-propanol, or in the absence of cyclase stimulators. The change in energy of activation found with hormones is abolished by 1-propanol. This change does not represent differences in hormone or substrate binding at different temperatures, but seems to reflect interactions among elements of the cyclase stimulation sequence. Similar changes in energy of activation were not observed for alkaline phosphatase, cyclic AMP-phosphodiesterase, 5'-nucleotidase, or ouabain-sensitive ATPase. Since the mole fraction of cholesterol in liver membranes is sufficiently high to preclude a phase change in bulk membrane lipids, our observation suggests either that cyclase is restricted to cholesterol-poor membrane regions or that the change in its energy of activation is largely restricted to protein components of the cyclase apparatus. The data are compatible with fundamental differences in the stimulation process(es) for the hormones (glucagon and epinephrine) as compared with those for fluoride and prostaglandin E(1).
我们描述了在胰高血糖素或肾上腺素存在的情况下，肝脏腺苷酸环化酶反应的活化能在32摄氏度时突然增加。在氟化物、前列腺素E(1)或1-丙醇存在的情况下，或者在没有环化酶刺激剂的情况下，这种增加并未出现。激素引起的活化能变化可被1-丙醇消除。这种变化并不代表激素或底物在不同温度下结合的差异，而似乎反映了环化酶刺激序列各元素之间的相互作用。对于碱性磷酸酶、环磷酸腺苷磷酸二酯酶、5'-核苷酸酶或哇巴因敏感的ATP酶，未观察到类似的活化能变化。由于肝细胞膜中胆固醇的摩尔分数足够高，足以排除整体膜脂的相变，我们的观察结果表明，要么环化酶局限于胆固醇含量低的膜区域，要么其活化能的变化主要局限于环化酶装置的蛋白质成分。这些数据与激素（胰高血糖素和肾上腺素）与氟化物和前列腺素E(1)的刺激过程存在根本差异相一致。
