Uzunov P, Lehne R, Revuelta A V, Gnegy M E, Costa E
Biochim Biophys Acta. 1976 Feb 13;422(2):326-34. doi: 10.1016/0005-2744(76)90144-3.
The effect of the endogenous protein activator on the kinetic characteristics of a highly purified, activator-deficient rat brain phosphodiesterase (EC 3.1.4.-) of a highly purified, activator-deficient rat brain phosphodiesterase (EC 3.1.4-) was studied. This enzyme preparation has only a high Km for cyclic AMP and a low Km for cyclic GMP. In the presence of 20 muM Ca2+, saturating concentrations of the activator decreased the Km of this enzyme for cyclic AMP from 350 muM to about 80 muM, without changing the V. The phosphodiesterase activator did not change the Km of phosphodiesterase for cyclic GMP; however, amoderate increase of V was seen. The activator lacks species specificity; the activator isolated from the bullfrog sympathetic chain produced the same qualitative and comparable quantitative changes in the kinetic properties of the purified rat brain phosphodiesterase. Cyclic GMP is a potent competitive inhibitor of the phosphodiesterase activation by the activator (Ki=1.8 muM), using cyclic AMP as a substrate. Cyclic AMP inhibits slightly the hydrolysis of cyclic GMP by phosphodiesterase in the presence of activator (Ki=155 muM) only.
研究了内源性蛋白质激活剂对高度纯化的、缺乏激活剂的大鼠脑磷酸二酯酶（EC 3.1.4.-）动力学特性的影响。这种酶制剂对环磷酸腺苷（cAMP）只有高Km值，对环磷酸鸟苷（cGMP）有低Km值。在20μM Ca2+存在的情况下，饱和浓度的激活剂使该酶对cAMP的Km值从350μM降至约80μM，而V不变。磷酸二酯酶激活剂未改变磷酸二酯酶对cGMP的Km值；然而，观察到V有适度增加。该激活剂缺乏物种特异性；从牛蛙交感神经链分离出的激活剂在纯化的大鼠脑磷酸二酯酶的动力学特性上产生了相同的定性和可比的定量变化。以cAMP为底物时，cGMP是激活剂激活磷酸二酯酶的有效竞争性抑制剂（Ki = 1.8μM）。仅在激活剂存在的情况下，cAMP轻微抑制磷酸二酯酶对cGMP的水解（Ki = 155μM）。
