Kolev K, Komorowicz E, Machovich R
Department of Biochemistry II, Semmelweis University of Medicine, Budapest, Hungary.
Blood Coagul Fibrinolysis. 1994 Dec;5(6):905-11. doi: 10.1097/00001721-199412000-00006.
The effect of heparin on the inactivation rates of fibrin-bound plasmin, miniplasmin and neutrophil leukocyte elastase (PMN-elastase) by their plasma inhibitors was studied. While plasmin and miniplasmin bound to fibrin are not inactivated by antithrombin, heparin (800 nM) makes these enzymes available for the inhibitor; the second-order rate constant increases from zero to 1.3 x 10(3) M-1 s-1 and 3.3 x 10(3) M-1 s-1, respectively. Heparin slightly increases the rate of fibrin-bound enzyme inactivation by plasmin inhibitor. alpha 1-Protease inhibitor, on the other hand, is unable to inactivate plasmin or miniplasmin bound to fibrin and heparin has no facilitating effect. In the case of PMN-elastase, heparin (300 nM) further increases enzyme protection against alpha 1-protease inhibitor; the rate constant decreases from 41 x 10(3) M-1 s-1 to 23 x 10(3) M-1 s-1. alpha 2-Macroglobulin inhibits fibrin-bound miniplasmin and PMN-elastase with a second-order rate constant of 1.8 x 10(4) M-1 s-1 and heparin (300 nM) increases the rate insignificantly for miniplasmin and by a factor of two for PMN-elastase. It is remarkable that plasmin bound to fibrin is not inhibited by alpha 2-macroglobulin independently of the presence of heparin. On the basis of the reported kinetic data a lifespan of 420 s for plasmin, 66 s for miniplasmin and 4 s for PMN-elastase was calculated, when the enzymes are bound to fibrin in the presence of the four protease inhibitors at physiological plasma concentration. If heparin is present (300 nM) these values decrease to 240 s for plasmin and 42 s for miniplasmin, whereas that of PMN-elastase is unchanged. Thus, the present in vitro kinetic model suggests an antifibrinolytic effect of heparin in a plasma milieu.
研究了肝素对纤维蛋白结合型纤溶酶、微型纤溶酶和中性粒细胞弹性蛋白酶（PMN-弹性蛋白酶）被其血浆抑制剂灭活速率的影响。虽然结合在纤维蛋白上的纤溶酶和微型纤溶酶不会被抗凝血酶灭活，但肝素（800 nM）可使这些酶与抑制剂结合；二级反应速率常数分别从零增加到1.3×10³ M⁻¹ s⁻¹和3.3×10³ M⁻¹ s⁻¹。肝素略微增加了纤溶酶抑制剂对纤维蛋白结合型酶的灭活速率。另一方面，α1-蛋白酶抑制剂无法灭活结合在纤维蛋白上的纤溶酶或微型纤溶酶，肝素也没有促进作用。对于PMN-弹性蛋白酶，肝素（300 nM）进一步增强了酶对α1-蛋白酶抑制剂的抵抗作用；反应速率常数从41×10³ M⁻¹ s⁻¹降至23×10³ M⁻¹ s⁻¹。α2-巨球蛋白以1.8×10⁴ M⁻¹ s⁻¹的二级反应速率常数抑制纤维蛋白结合型微型纤溶酶和PMN-弹性蛋白酶，肝素（300 nM）对微型纤溶酶的速率增加不显著，对PMN-弹性蛋白酶的速率增加两倍。值得注意的是，无论是否存在肝素，结合在纤维蛋白上的纤溶酶都不会被α2-巨球蛋白抑制。根据所报道的动力学数据，当这些酶在生理血浆浓度下的四种蛋白酶抑制剂存在时与纤维蛋白结合时，计算出纤溶酶的寿命为420秒，微型纤溶酶为66秒，PMN-弹性蛋白酶为4秒。如果存在肝素（300 nM），这些值对于纤溶酶降至240秒，对于微型纤溶酶降至42秒，而PMN-弹性蛋白酶的寿命不变。因此，目前的体外动力学模型表明肝素在血浆环境中具有抗纤溶作用。
