Interaction Of Plasminogen With Human Platelets

血凝块的溶解（纤溶）需要纤溶酶，一种由组织纤溶酶原激活剂（tPA）激活纤溶酶原而产生的蛋白酶。已知纤溶酶原和tPA都与血小板表面结合，在那里它们的相互作用大大加速。因此，血小板是纤溶的重要促进剂。我们实验室一直在详细研究纤溶酶原与血小板的结合。我们使用经典的平衡结合实验，目的是确定结合位点的数量和结合亲和力。我们还将生物素化的纤溶酶原与血小板进行化学交联，然后通过Western blotting检测纤溶酶原受体复合物，目的是鉴定将纤溶酶原与活化细胞和静息细胞结合的血小板膜蛋白。文献表明，血小板活化可增强纤溶酶原，且这种增强的结合不是直接与血小板结合，而是与血小板结合的纤维蛋白结合。然而，我们的数据表明存在直接与血小板膜蛋白IIIa结合的纤溶酶原，也可能与IIb结合。当血小板被凝血酶激活时，它们的纤溶酶原结合位点的数量似乎从每个细胞大约12万个减少到每个细胞6万个，但结合亲和力增加了几倍。

Dissolution of blood clots (fibrinolysis) requires plasmin, a protease derived from the activation of plasminogen by tissue plasminogen activator (tPA). Both plasminogen and tPA are known to bind to the surface of platelets, where their interaction becomes greatly accelerated. Therefore, platelets are important promoters of fibrinolysis. Our laboratory has been examining plasminogen binding to platelets in some detail. We use classical equilibrium binding experiments with the goal of establishing the number of binding sites and the binding affinity. We are also chemically crosslinking biotinylated plasminogen to platelets and then testing for plasminogen-receptor complexes by Western blotting, with the goal of identifying the platelet membrane protein(s) that binds plasminogen to activated and resting cells. The literature indicates that platelet activation enhances plasminogen and that the increased binding is not directly to the platelets but to platelet-bound fibrin. However, our data suggest that there is direct plasminogen binding to the platelet membrane protein IIIa and possibly to IIb. When platelets are activated with thrombin, the number of their plasminogen binding sites appears to decrease from approximately 120,000 per cell to 60,000 per cell, but the binding affinity increases several fold.