Hartshorne D J
J Gen Physiol. 1970 May;55(5):585-601. doi: 10.1085/jgp.55.5.585.
Troponin B is an inhibitor of the Mg(++)-activated ATPase activity of actomyosin. The inhibitory effect, which is observed, however, depends upon whether tropomyosin is also present. In the absence of tropomyosin the inhibition by troponin B is markedly reduced by increasing the ionic strength from 0.03 to 0.07, but is not affected by calcium up to a concentration of 10(-4)M. Troponin A relieves the inhibition in both the absence and presence of calcium, an effect which is also shown by many polyanions and is illustrated by using RNA. Tropomyosin enhances the inhibitory effect of troponin B and renders it more resistant to increasing ionic strength but it does not make the inhibition calcium-sensitive. However, when troponin A or low concentrations of polyanions are added to troponin B and tropomyosin, the actomyosin ATPase activity becomes calcium-sensitive; i.e., in the presence of tropomyosin, troponin A or polyanions do not relieve the inhibitory action of troponin B in the absence of calcium but only in its presence. In marked contrast to this is the effect of troponin A in the absence of tropomyosin where it neutralizes the effect of troponin B under all conditions. Thus troponin A and the polyanions both confer calcium regulation on the troponin B-tropomyosin system. The similar effects exhibited by troponin A and the polyanions suggest that the addition of net negative charge to troponin B is an important factor in the conferral of calcium sensitivity. It is also clear that tropomyosin is an essential component of the regulatory mechanism.
肌钙蛋白B是肌动球蛋白的Mg(++)激活的ATP酶活性的抑制剂。然而，所观察到的抑制作用取决于原肌球蛋白是否也存在。在没有原肌球蛋白的情况下，将离子强度从0.03增加到0.07可显著降低肌钙蛋白B的抑制作用，但在钙浓度高达10(-4)M时不受影响。在有无钙的情况下，肌钙蛋白A均可解除抑制作用，许多聚阴离子也表现出这种作用，以RNA为例说明。原肌球蛋白增强了肌钙蛋白B的抑制作用，并使其对离子强度增加更具抗性，但它不会使抑制作用对钙敏感。然而，当将肌钙蛋白A或低浓度的聚阴离子添加到肌钙蛋白B和原肌球蛋白中时，肌动球蛋白ATP酶活性变得对钙敏感；即，在有原肌球蛋白的情况下，肌钙蛋白A或聚阴离子在没有钙时不会解除肌钙蛋白B的抑制作用，而仅在有钙时解除。与此形成鲜明对比的是，在没有原肌球蛋白的情况下，肌钙蛋白A在所有条件下均中和肌钙蛋白B的作用。因此，肌钙蛋白A和聚阴离子均赋予肌钙蛋白B-原肌球蛋白系统钙调节能力。肌钙蛋白A和聚阴离子表现出的相似作用表明，向肌钙蛋白B添加净负电荷是赋予钙敏感性的重要因素。同样明显的是，原肌球蛋白是调节机制的重要组成部分。
