Tersariol I L, Dietrich C P, Nader H B
Disciplina de Biologia Molecular, Escola Paulista de Medicina (UNIFESP), São Paulo, Brasil.
Eur J Biochem. 1997 Apr 1;245(1):40-6. doi: 10.1111/j.1432-1033.1997.00040.x.
Heparin and its enzymatic fragments, prepared by degradation of heparin with heparinase from Flavobacterium heparinum, were capable of inhibiting the actomyosin-ATPase activity obtained from striated and smooth vascular muscles. Heparin did not inhibit the myosin-ATPase activity in absence of actin. The results show that heparin changes the step of ATP hydrolysis of the complex actomyosin-ATPase by uncoupling the conformational transition on the myosin-head induced by actin upon the nucleotide-binding site. This mechanism is cooperative and dependent on conformational states of actomyosin complex which in turn is regulated by ATP and calcium levels. It was observed that in the presence of ATP, actin does not compete with heparin for binding to myosin showing that heparin and actin have different binding sites on myosin. The binding of heparin and ATP is cooperative suggesting that the nucleotide binding leads to an exposition of a second heparin-binding site. However, in the absence of ATP, actin competes with heparin for a binding site on the myosin. These results strongly suggest that in the weakly binding state of actin to myosin, the binding of heparin is powerful and in the rigor state its binding is decreased.
肝素及其通过用来自肝素黄杆菌的肝素酶降解肝素制备的酶促片段，能够抑制从横纹肌和平滑血管肌获得的肌动球蛋白 - ATP酶活性。在没有肌动蛋白的情况下，肝素不抑制肌球蛋白 - ATP酶活性。结果表明，肝素通过解偶联肌动蛋白在核苷酸结合位点上诱导的肌球蛋白头部的构象转变，改变了复合肌动球蛋白 - ATP酶的ATP水解步骤。这种机制是协同的，并且依赖于肌动球蛋白复合物的构象状态，而肌动球蛋白复合物又受ATP和钙水平的调节。据观察，在ATP存在的情况下，肌动蛋白不与肝素竞争结合肌球蛋白，这表明肝素和肌动蛋白在肌球蛋白上具有不同的结合位点。肝素与ATP的结合是协同的，这表明核苷酸结合导致第二个肝素结合位点的暴露。然而，在没有ATP的情况下，肌动蛋白与肝素竞争肌球蛋白上的一个结合位点。这些结果强烈表明，在肌动蛋白与肌球蛋白的弱结合状态下，肝素的结合很强，而在僵直状态下其结合减少。
