Interaction Of Plasminogen With Human Platelets

血凝块的溶解（纤维蛋白溶解）需要纤溶酶，纤溶酶是一种来源于组织纤溶酶原激活剂（tPA）激活纤溶酶原的蛋白酶。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，血小板是纤维蛋白溶解的重要促进剂。本实验室通过平衡结合实验和血小板依赖性纤溶酶原激活速率测定两种方法研究了纤溶酶原和血小板的相互作用。我们已经发现，用凝血酶刺激血小板增加了纤溶酶原与血小板表面的高亲和力结合，并大大加速了在血小板存在下纤溶酶原转化为纤溶酶的速率。用除去C-末端赖氨酸的羧肽酶B处理过的血小板缺乏高亲和力纤溶酶原结合，并显示支持纤溶酶原转化的能力低得多。抗纤维蛋白原抗体的F（ab '）2片段也能降低纤溶酶原结合和转化，但其作用不如羧肽酶作用显著。我们的目标有三个方面：（1）确定对羧肽酶和抗纤维蛋白原敏感的结合位点的数量和亲和力;（2）确定这些位点类别是否彼此不同;（3）确定这些位点类别在促进纤溶酶原转化为纤溶酶中的相对重要性。

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 the interaction of plasminogen and platelets with two types of assays: equilibrium binding experiments and rate measurements of platelet-dependent plasminogen activation. We have found that stimulation of platelets with thrombin increases high-affinity binding of plasminogen to the platelet surface and greatly accelerates the rate of plasminogen conversion to plasmin in the presence of platelets. Platelets that have been treated with carboxypeptidase B, which removes C-terminal lysines, lack high-affinity plasminogen binding and demonstrate much less ability to support plasminogen conversion. Plasminogen binding and conversion are also reduced by F(ab')2 fragments of anti-fibrinogen antibodies, but the effect is not as marked as the carboxypeptidase effect. Our goal is three-fold: (1) to determine the number and affinity of binding sites sensitive to carboxypeptidase and to anti-fibrinogen; (2) to establish whether these classes of sites are different from each other; and (3) to determine the relative importance of these classes of sites in promoting plasminogen conversion to plasmin.