Pletcher C H, Cunningham M, Nelsestuen G L
Biochim Biophys Acta. 1985 Jan 28;838(1):106-13. doi: 10.1016/0304-4165(85)90256-9.
Kinetic characteristics of several heparin preparations and substitute heparins were determined to help understand the bases for activity differences. Several materials were highly active in factor Xa inhibition and the reaction rate at constant factor Xa concentration appeared to be predicted by the extent of intrinsic antithrombin III fluorescence change induced by the polysaccharide. Heparin fractions of different molecular weight and affinity for antithrombin III showed similar kinetic parameters in catalysis of the thrombin-antithrombin III reaction when these parameters were expressed on the basis of antithrombin III-binding heparin. The latter was determined by stoichiometric titration of the antithrombin III fluorescence change by the heparin preparation. However, the various heparin fractions showed very different specific activities per mg of total polysaccharide. This indicated that functional heparin molecules had similar kinetic properties regardless of size or antithrombin III-binding affinity and is possible because the Km for antithrombin III is determined by diffusion rather than by binding affinity. Substitute heparins and depolymerized heparin were poor catalysts for thrombin inhibition, due at least partially to their affinity for thrombin. This latter binary interaction inhibits thrombin reaction in the heparin-catalyzed reaction.
测定了几种肝素制剂和替代肝素的动力学特征，以帮助理解活性差异的基础。几种物质在抑制因子Xa方面具有高活性，并且在恒定因子Xa浓度下的反应速率似乎可通过多糖诱导的内在抗凝血酶III荧光变化程度来预测。当基于抗凝血酶III结合肝素表达这些参数时，不同分子量和对抗凝血酶III亲和力的肝素级分在催化凝血酶 - 抗凝血酶III反应中显示出相似的动力学参数。后者通过用肝素制剂对抗凝血酶III荧光变化进行化学计量滴定来确定。然而，各种肝素级分每毫克总多糖显示出非常不同的比活性。这表明功能性肝素分子无论大小或抗凝血酶III结合亲和力如何都具有相似的动力学性质，这是可能的，因为抗凝血酶III的Km由扩散而非结合亲和力决定。替代肝素和解聚肝素是凝血酶抑制的不良催化剂，至少部分是由于它们对凝血酶的亲和力。后一种二元相互作用在肝素催化的反应中抑制凝血酶反应。
