Takada A, Sugawara Y, Takada Y
Department of Physiology, Hamamatsu University, School of Medicine, Shizuoka-ken, Japan.
Haemostasis. 1989;19(1):26-31. doi: 10.1159/000215885.
The activation rate of Glu-plasminogen (Glu-plg) by urokinase (UK) was enhanced in the presence of either tranexamic acid or fibrin with an increase in the catalytic rate constant (kcat). The maximum increase in kcat was obtained at 0.5 mM of tranexamic acid and 0.1 microM of fibrin. Km did not change. The addition of fibrin to 1 mM tranexamic acid resulted in a further increase in kcat of the UK activation of Glu-plg. On the other hand, the addition of tranexamic acid to 0.1 microM fibrin further increased kcat of the UK activation of Glu-plg. Thus, stimulatory effects were observed on the activation of Glu-plg by UK in the simultaneous presence of tranexamic acid and fibrin. Fibrin-binding sites on the kringle 5 of Glu-plg may be involved in the further increase in the activation rate of Glu-plg by UK in the presence of both fibrin and tranexamic acid in comparison to that in the presence of tranexamic acid alone. Possibly, the Glu-plg binding with both tranexamic acid and fibrin (at kringle 5) may be most effectively activated by UK. It is also suggested that two molecules of Glu-plg bind to one molecule of fibrin monomer.
在氨甲环酸或纤维蛋白存在的情况下，尿激酶（UK）对谷氨酸纤溶酶原（Glu - plg）的激活率会提高，催化速率常数（kcat）增加。在0.5 mM氨甲环酸和0.1 μM纤维蛋白时获得kcat的最大增加。Km不变。向1 mM氨甲环酸中添加纤维蛋白会导致UK激活Glu - plg的kcat进一步增加。另一方面，向0.1 μM纤维蛋白中添加氨甲环酸会进一步增加UK激活Glu - plg的kcat。因此，在氨甲环酸和纤维蛋白同时存在的情况下，观察到UK对Glu - plg激活有刺激作用。与仅存在氨甲环酸相比，在纤维蛋白和氨甲环酸同时存在的情况下，Glu - plg kringle 5上的纤维蛋白结合位点可能参与UK对Glu - plg激活率的进一步增加。可能，与氨甲环酸和纤维蛋白（在kringle 5处）都结合的Glu - plg可能被UK最有效地激活。还表明两分子的Glu - plg与一分子纤维蛋白单体结合。
