Interaction Of Plasminogen With Human Platelets

血栓的溶解(纤溶)需要纤溶酶，这是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。纤溶酶原和组织型纤溶酶原激活剂都能结合到血小板表面，在那里它们的相互作用会大大加速。因此，血小板是纤溶系统的重要促进剂。我们的实验室一直在比较详细地检测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化学交联到血小板上，然后通过Western blotting检测纤溶酶原受体复合体，目的是鉴定将纤溶酶原结合到激活和静止细胞上的血小板膜蛋白(S)。文献表明，血小板激活增强了纤溶酶原，增加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，无论是在静息时还是在激活时，都有纤溶酶原直接与血小板结合。激活后结合位点的数量似乎没有变化，但结合亲和力大大增加。然而，单抗对纤溶酶原与静息和活化的血小板结合的影响是不同的。

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 platelets, both when they are resting and when they are activated. The number of binding sites appears to be unchanged by activation but binding affinity is greatly increased. However, the effect of monoclonal antibodies on plasminogen binding to resting and activated platelets is different.