Nosaka S, Onji T, Shibata N
Biochim Biophys Acta. 1984 Aug 14;788(3):290-7. doi: 10.1016/0167-4838(84)90040-2.
In skeletal muscle, the physiological role of tropomyosin has been assumed to be the 'blocking' of the actin-myosin interaction. In smooth muscle and platelet, however, tropomyosin was shown to 'enhance' the interaction. To investigate the reason for this apparent contradiction, we carried out recombination experiments using reconstituted actomyosins and different tropomyosins. Tropomyosins from skeletal muscle, arterial smooth muscle and platelet were recombined with skeletal, arterial and platelet myosins. The effects of tropomyosins on the actin-activated ATPase activities of myosins were then examined. The results are as follows. (i) Although tropomyosins from artery and platelet are distinctively different in molecular weight, they are interchangeable in enhancing the ATPase activities of both arterial and platelet actomyosins. The enhancement, however, is reduced by increasing the concentration of Mg X ATP and decreasing the concentration of myosin. (ii) Arterial and platelet tropomyosins are not capable of inhibiting the ATPase activity of skeletal actomyosin. (iii) Skeletal tropomyosin enhances arterial and platelet actomyosin ATPase activities in the same way as arterial and platelet tropomyosins. The results indicate that the major determinant of the effect of tropomyosin on the actomyosin-ATPase activity is the state of actomyosin. We suggest that any tropomyosin enhances the actin-activated ATPase activity of myosin recombined with skeletal actin, under the condition where actin and myosin form a 'rigor' (tight) complex.
在骨骼肌中，原肌球蛋白的生理作用被认为是“阻断”肌动蛋白与肌球蛋白的相互作用。然而，在平滑肌和血小板中，原肌球蛋白却被证明会“增强”这种相互作用。为了探究这一明显矛盾的原因，我们使用重组的肌动球蛋白和不同的原肌球蛋白进行了重组实验。将来自骨骼肌、动脉平滑肌和血小板的原肌球蛋白分别与骨骼肌、动脉和血小板肌球蛋白进行重组。然后检测原肌球蛋白对肌球蛋白的肌动蛋白激活ATP酶活性的影响。结果如下：（i）尽管来自动脉和血小板的原肌球蛋白在分子量上有显著差异，但它们在增强动脉和血小板肌动球蛋白的ATP酶活性方面是可互换的。然而，通过增加MgXATP的浓度和降低肌球蛋白的浓度，这种增强作用会减弱。（ii）动脉和血小板原肌球蛋白不能抑制骨骼肌肌动球蛋白的ATP酶活性。（iii）骨骼肌原肌球蛋白增强动脉和血小板肌动球蛋白ATP酶活性的方式与动脉和血小板原肌球蛋白相同。结果表明，原肌球蛋白对肌动球蛋白-ATP酶活性影响的主要决定因素是肌动球蛋白的状态。我们认为，在肌动蛋白和肌球蛋白形成“强直”（紧密）复合物的条件下，任何原肌球蛋白都会增强与骨骼肌肌动蛋白重组的肌球蛋白的肌动蛋白激活ATP酶活性。
