<Ca^(2+)> regulatory mechanism of smooth muscle contraction

钙调蛋白依赖的肌球蛋白轻链的磷酸化被广泛认为是钙调节的平滑肌收缩激活的分子机制。然而，我们提出肌动蛋白结合蛋白是真正的激活剂，它被命名为‘Leiottin’。在目前的研究中，获得了以下结果，所有这些结果都证明了‘激酶活性’和收缩之间的差异。刺激活性1)用Lt；V_8&gt；蛋白酶、CANP或胰酶消化‘激活组分’几乎不影响其收缩刺激活性，但几乎完全破坏其收缩刺激活性。2)化学修饰‘激活组分’的赖氨酸、酪氨酸或半胱氨酸残基导致其收缩刺激活性丧失，但抑制其活性。3)随着pH从6.8增加到8.0，激动酶活性降低，而收缩刺激活性在该pH范围内几乎相同。

Phosphorylation of myosin light chains by Ca-calmodulin dependent kinase is now widely believed to be the molecular mechanism of Ca-regulated activation of smooth muscle contraction. We have, however, proposed that the actin-binding protein, named 'leiotonin', is the real activator. In the present study, following results have been obtained, all of which demonstrate the discrepancy between 'kinase activity' and contraction-. stimulating activity.1) Digestion of 'activator fraction' by <V_8> protease, CANP or trypsin scarcely affected its kinase activity, but almost completely destroyed its contraction-stimulating activity.2) Chemical modification of Lys, Tyr or Cys residues of 'activator fraction' resulted in the loss of its contraction-stimulating activity, while sparing its kinase activity.3) Kinase activity was decreased with increase in pH from 6.8 to 8.0, while contraction-stimulating activity was almost the same in that range of pH.