Petrella V J, Zenser T V
Biochim Biophys Acta. 1976 Feb 24;421(2):237-45. doi: 10.1016/0304-4165(76)90290-7.
Kinetic parameters of mouse thymocyte adenylate cyclase activity were determined. NaF and cholera toxin stimulated adenylate cyclase. Stimulation by either agent did not change the pH or Mg2+ optima relative to control (unstimulated cyclase). The Km value for ATP of adenylate cyclase stimulated by NaF was significantly reduced from control. By contrast, cholera toxin treatment did not change the Km relative to control. Adenylate cyclase, when stimulated by NaF, had an optimum for Mn2+ alone, or Mn2+ in combination with Mg2+, at least twice that of control. In contrast, cyclase activity prepared from cells treated with cholera toxin remained unchanged with regard to these divalent cations when compared to control. Addition of NaF to adenylate cyclase prepared from cells treated with cholera toxin resulted in a significant reduction (30%) in activity suggesting that both NaF and cholera toxin were acting on the same cyclase. NaF inhibition of cholera toxin-stimulated activity was shown to be a direct interaction of fluoride on the stimulated cyclase enzyme. This inhibition appeared to be immediate and independent on pH, Mg2+ or ATP concentrations. Although NaF inhibition was lost when Mn2+ was present in the reaction mixture, the activity expressed by addition of NaF to cyclase prepared from cholera toxin-treated cells was much less than by addition of NaF to control. As observed with cholera toxin stimulation alone, activity expressed by the inhibited enzyme (cholera toxin treated + NaF) exhibited a Km for ATP and an optimum for Mn2+ alone or in combination with Mg2+ similar to control.
测定了小鼠胸腺细胞腺苷酸环化酶活性的动力学参数。氟化钠（NaF）和霍乱毒素可刺激腺苷酸环化酶。相对于对照（未刺激的环化酶），这两种试剂的刺激均未改变pH或镁离子（Mg2+）的最适浓度。NaF刺激的腺苷酸环化酶对ATP的米氏常数（Km）值相对于对照显著降低。相比之下，霍乱毒素处理并未改变相对于对照的Km值。当受到NaF刺激时，腺苷酸环化酶单独对锰离子（Mn2+）或与Mg2+结合时的最适浓度，至少是对照的两倍。相反，与对照相比，用霍乱毒素处理的细胞所制备的环化酶活性在这些二价阳离子方面保持不变。向用霍乱毒素处理的细胞所制备的腺苷酸环化酶中添加NaF，导致活性显著降低（30%），这表明NaF和霍乱毒素作用于同一种环化酶。NaF对霍乱毒素刺激活性的抑制作用被证明是氟化物与受刺激的环化酶直接相互作用。这种抑制作用似乎是即时的，且与pH、Mg2+或ATP浓度无关。尽管当反应混合物中存在Mn2+时NaF的抑制作用消失，但向用霍乱毒素处理的细胞所制备的环化酶中添加NaF所表现出的活性，远低于向对照中添加NaF所表现出的活性。正如单独用霍乱毒素刺激时所观察到的，受抑制的酶（霍乱毒素处理 + NaF）所表现出的对ATP的Km值以及单独对Mn2+或与Mg2+结合时的最适浓度，与对照相似。
