纤维蛋白对尿激酶原激活纤溶酶原反应动力学的影响

反应体系中存在的纤维蛋白（fibrin）对尿激酶（UK）、scu-PA以及组织型纤溶酶原激活剂（t-PA）激活纤溶酶原（plasminogen）的反应有不同的作用：UK、t-PA激活plasminogen的反应可被反应体系中存在的fibrin所加强；fibrin对scu-PA激活plasminogen反应的动力学常数无明显影响；但对小分子质量scu-PA与单链抗体的嵌合分子激活plasminogen的反应起明显的抑制作用.为确定反应体系中存在的fibrin对scu-PA的K区插入突变体-InB激活plasminogen反应的影响，测定了在反应体系中存在fibrin的情况下的InB激活plasminogen反应的K_m^fibrin以及k_cat^fibrin.K_m^fibrin＝4.2 μmol·L^-1，远远大于无fibrin时的K_m＝0.379 μmol·L^-1，说明有fibrin存在时突变体InB与天然底物plasminogen的亲和性降低了.k_cat^fibrin＝0.107 s^-1，也远远大于无fibrin时k_cat＝0.0165 s^-1，说明有fibrin存在时突变体InB对plasminogen的反应活性增强了.原因可能是：与fibrin结合的plasminogen的构象发生了有利于被纤溶酶原激活剂水解的变化.

The Influence of Fibrin on the Reaction of Plasminogen Activation by Mutant of Pro-Urokinase

Because the influence of fibrin on the reaction of plasm inogen activation by various plasminogen activators is different, the kinetic co nstant of the reaction of plasminogen activation catalyzed by InB with and witho ut fibrin were detected. The result is: Kfibrinm＝4.2 μmol*L -1，greater than the normal Km=0.379 μmol*L-1; kfib rincat＝0.107 s-1，greater than the normal kcat=0.0165 s-1. The results suggest that existence of fibrin in the reaction system of plasminogen activation depress the affinity between InB and plasminog en, but accelerates the hydrolysis of plasminogen by InB. The count up effect is inhibition.