Kinetics of the heparin-enhanced antithrombin III/thrombin reaction. Evidence for a template model for the mechanism of action of heparin.
Kinetics of the heparin-enhanced antithrombin III/thrombin reaction. Evidence for a template model for the mechanism of action of heparin.
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DOI：
10.1016/s0021-9258(18)34385-0
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发表时间：
1982-07
期刊：
影响因子：
--
通讯作者：
M. Griffith
中科院分区：
文献类型：
--
作者：
M. Griffith
肝素增强的抗凝血酶III/凝血酶反应进行了研究，旨在确定肝素的作用机制的动力学模型的有效性的各种条件下。所观察到的第二阶速率常数k&值的凝血酶抑制抗凝血酶I11的肝素浓度的存在和不存在的变化量的活性位点封闭的凝血酶的函数确定。在没有活性位点封闭的凝血酶的情况下，kZb.值随着肝素浓度增加至约M而增加。随着肝素浓度的增加，k：bb。价值逐渐下降。在存在活性位点封闭的凝血酶的情况下，肝素浓度依赖性曲线在低肝素浓度（小于M）下向右移动。在较高肝素浓度（大于5.0 × 10 - 1 M）下，活性位点封闭的凝血酶对凝血酶抑制速率没有可测量的影响。还进行了实验，在存在和不存在的活性位点封闭的凝血酶，以确定抗凝血酶I11的肝素增强的抗凝血酶III/凝血酶反应的浓度依赖性。结果表明，在肝素存在下，抗凝血酶I11对凝血酶抑制率的增强是由于两种蛋白质同时结合到同一肝素分子上。在先前报道的肝素作用机制模型中，只有模板（三元复合物）模型描述了实验结果。模板模型，因此，推导出数学术语和理论数据计算，以测试模型的可能的有效性。使用肝素-凝血酶和肝素-抗凝血酶I11解离常数值分别为3.5 × 10 - 1 M和1.0 × 10 - 1 M，获得了理论数据和实验数据之间非常合理的相关性。利用该模型，反应相对于三元（抗凝血酶III-肝素-凝血酶）复合物的浓度是一级的，表观一级速率常数k '值为800 min-1。得出的结论是，目前，模板模型提供了最简单的工作模型的作用机制，肝素在加速凝血酶抑制抗凝血酶111。
The heparin-enhanced antithrombin III/thrombin reaction was studied under a variety of conditions designed to determine the validity of kinetic models for the mechanism of action of heparin. The observed second order rate constant k& values for thrombin inhibition by antithrombin I11 were determined as a function of heparin concentration in the presence and absence of varying amounts of active site-blocked thrombin. In the absence of active site-blocked thrombin, the kZb. value increased as the concentration of heparin was increased to approximately M. With higher heparin concentration, the k: bb. value progressively decreased. In the presence of active site-blocked thrombin, the heparin concentration dependence curve was shifted to the right at low heparin concentration (less than M). With higher heparin concentration (greater than 5.0 X lo-’M) there was no measurable effect of active site-blocked thrombin on the rate of thrombin inhibition. Experiments were also conducted in the presence and absence of active site-blocked thrombin to determine the antithrombin I11 concentration dependence for the heparin-enhanced antithrombin III/thrombin reaction. The results suggested that the enhanced rate of thrombin inhibition by antithrombin I11 in the presence of heparin is due to the simultaneous binding of both proteins to the same heparin molecule. Of the previously reported models for the mechanism of action of heparin, only the template (ternary complex) model appeared to describe the experimental results. The template model was, therefore, derived in mathematical terms and theoretical data calculated to test the possible validity of the model. Using heparin-thrombin and heparin-antithrombin I11 dissociation constant values of 3.5 X lo-’M and 1.0 X M, respectively, a very reasonable correlation between theoretical data and experimental data was obtained. With this model, the reaction is first order with respect to the concentration of the ternary (antithrombin III-heparin-thrombin) complex, with an apparent first order rate constant k’value of 800 min”. It was concluded that, at the present time, the template model provides the simplest working model for the mechanism of action of heparin in accelerating thrombin inhibition by antithrombin 111.