Correlation between the inhibition of the acto-heavy meromyosin ATPase and the binding of tropomyosin to F-actin: effects of Mg2+, KCl, troponin I, and troponin C.
Correlation between the inhibition of the acto-heavy meromyosin ATPase and the binding of tropomyosin to F-actin: effects of Mg2+, KCl, troponin I, and troponin C.
复制标题
重肌球蛋白 ATP 酶的抑制与原肌球蛋白与 F-肌动蛋白结合之间的相关性：Mg2、KCl、肌钙蛋白 I 和肌钙蛋白 C 的作用。
作者：
B. L. Eaton;D. Kominz;E. Eisenberg
当化学计量量的原肌球蛋白 (TM) 在 2 mM ATP 存在下与 F-肌动蛋白结合时，MG2+ 激活的重肌球蛋白 (HMM) ATP 酶在 5 mM MgCl2-30 mM KCl 中被抑制约 60%。如果 MgCl2 的浓度降低至 1 mM，抑制作用就会消失，因为 TM 不再与 F-肌动蛋白结合。将 KCl 浓度增加至 100 mM 可恢复结合和抑制。因此，如果 HMM 被 ATP 饱和，TM 单独与 F-肌动蛋白结合会引起 ATP 酶的显着抑制。 （当HMM未饱和时，TM激活ATPase）。当单独的 TM 可以化学计量地结合 F-肌动蛋白时，添加肌钙蛋白 I (TN-I) 将抑制作用从 60% 增加到约 85%，但 TM 与 F-肌动蛋白的结合不受影响。在TM单独既不抑制acto-HMM ATPase也不与F-肌动蛋白结合的条件下，TN-I加TM引起的抑制仍然接近100%。这些条件下的直接结合研究表明，TN-I 诱导 TM 和 F-肌动蛋白之间的结合。 TN-I 具有双重作用：首先，TN-I 可以诱导 TM 与 F-肌动蛋白结合，从而抑制 ATP 酶；其次，TN-I本身可以协同增强对ATPase的抑制作用。在不存在CA2+的情况下添加TN-C对第一个作用仅具有有限的作用，但似乎能够完全阻断由TN-I引起的协同抑制，使得残余抑制仅是保持结合的TM的功能。
When stoichiometric amounts of tropomyosin (TM) are bound to F-actin in the presence of 2 mM ATP, the MG2+-activated acto-heavy meromyosin (HMM) ATPase is inhibited by about 60% in 5 mM MgCl2-30 mM KCl. If the concentration of MgCl2 is reduced to 1 mM, the inhibition disappears because TM no longer binds to F-actin. Increasing the concentration of KCl to 100 mM restores both the binding and the inhibition. Thus, the binding of TM alone to F-actin causes significant inhibition of the ATPase provided that the HMM is saturated with ATP. (When the HMM is not saturated, TM activates the ATPase). When TM alone can bind stoichiometrically to F-actin, addition of troponin I (TN-I) increases the inhibition from 60% to about 85%, but the TM binding to F-actin is not affected. Under conditions such that TM alone neither inhibits the acto-HMM ATPase nor binds to F-actin, the inhibition caused by TN-I plus TM still approaches 100%. Direct binding studies under these conditions show that TN-I induces binding between TM and F-actin. A dual role for TN-I is proposed: first, TN-I can induce TM to bind to F-actin, causing inhibition of the ATPase; and second, TN-I can itself enhance the inhibition of the ATPase in a cooperative manner. The addition of TN-C in the absence of CA2+ has only a limited effect on the first role, but seems to be able to block completely the cooperative inhibition caused by TN-I such that the residual inhibition is a function only of the TM which remains bound.