肌钙蛋白-原肌球蛋白的作用机制。抑制肌动球蛋白ATP酶活性，而不抑制肌球蛋白与肌动蛋白的结合。
Mechanism of action of troponin . tropomyosin. Inhibition of actomyosin ATPase activity without inhibition of myosin binding to actin.
作者信息
Chalovich J M, Chock P B, Eisenberg E
出版信息
J Biol Chem. 1981 Jan 25;256(2):575-8.
The regulation of vertebrate skeletal muscle contraction by the troponin . tropomyosin complex is generally thought to be the result of tropomyosin physically blocking the myosin binding site of actin in the absence of Ca2+. This mechanism was tested during steady state ATP hydrolysis by comparing the degree of association of myosin subfragment 1 (S-1) with the actin . troponin . tropomyosin complex in the absence and presence of Ca2+. Binding in the presence of ATP was determined by stopped flow absorbance measurements at 25 degrees C. Although the steady state ATPase rate was reduced 96% in the absence of Ca2+, the association constant of S-1 with regulated actin was virtually the same in the absence of Ca2+ (1.3 X 10(4) M-1) as in the presence of Ca2+ (2.3 X 10(4) M-1). The association constant of S-1 to regulated actin in the presence of Ca2+ was similar to the association constant of S-1 to unregulated actin. These results suggest that the troponin . tropomyosin complex does not inhibit the actin-activated ATPase activity by preventing the binding of S-1 . ATP or S-1 . ADP . Pi to actin; rather, it may act by blocking the release of Pi from the acto-S-1 . ADP . Pi complex.
肌钙蛋白 - 原肌球蛋白复合物对脊椎动物骨骼肌收缩的调节通常被认为是在没有Ca2+的情况下，原肌球蛋白通过物理方式阻断肌动蛋白的肌球蛋白结合位点的结果。在稳态ATP水解过程中，通过比较在没有Ca2+和存在Ca2+的情况下肌球蛋白亚片段1（S-1）与肌动蛋白 - 肌钙蛋白 - 原肌球蛋白复合物的结合程度，对这一机制进行了测试。在25℃下通过停流吸光度测量来确定ATP存在时的结合情况。尽管在没有Ca2+的情况下稳态ATP酶速率降低了96%，但在没有Ca2+（1.3×10⁴ M⁻¹）和存在Ca2+（2.3×10⁴ M⁻¹）时，S-1与调节型肌动蛋白的结合常数实际上是相同的。在存在Ca2+的情况下，S-1与调节型肌动蛋白的结合常数类似于S-1与非调节型肌动蛋白的结合常数。这些结果表明，肌钙蛋白 - 原肌球蛋白复合物不是通过阻止S-1·ATP或S-1·ADP·Pi与肌动蛋白的结合来抑制肌动蛋白激活的ATP酶活性；相反，它可能是通过阻断Pi从肌动蛋白 - S-1·ADP·Pi复合物中的释放来发挥作用。
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