Collen D, Zamarron C, Lijnen H R, Hoylaerts M
J Biol Chem. 1986 Jan 25;261(3):1259-66.
The kinetics of the activation of plasminogen by recombinant pro-urokinase obtained by expression of human urokinase cDNA in Escherichia coli was studied. The conversion of pro-urokinase (U) and plasminogen (P) to urokinase (u) and plasmin (p) is represented by a sequence of three reactions which each obey Michaelis-Menten kinetics, i.e. (Formula: see text). In this model, pro-urokinase formally behaves as an enzyme in Reaction I and as a substrate in reaction II. The experimentally measured overall rates of formation of urokinase and plasmin are in good agreement with those calculated from the kinetic parameters and the initial concentrations of pro-urokinase and plasminogen, confirming the validity of the model. It appears that recombinant pro-urokinase is an equally potent activator of plasminogen (k2/Km = 0.05 microM-1 s-1), as in urokinase (k"2/K"m = 0.02 microM-1 s-1). This is due to the fact that the proenzyme, which is virtually inactive toward low Mr substrates for urokinase, forms an intermediate of the Michaelis-Menten type with plasminogen, with a much higher affinity than that of the active enzyme with its substrate. This is an exceptional phenomenon among the serine proteases.
对通过在大肠杆菌中表达人尿激酶cDNA获得的重组尿激酶原激活纤溶酶原的动力学进行了研究。尿激酶原（U）和纤溶酶原（P）向尿激酶（u）和纤溶酶（p）的转化由三个反应序列表示，每个反应均符合米氏动力学，即（公式：见原文）。在该模型中，尿激酶原在反应I中形式上作为一种酶，在反应II中作为一种底物。实验测得的尿激酶和纤溶酶的总体生成速率与根据动力学参数以及尿激酶原和纤溶酶原的初始浓度计算得到的速率高度一致，证实了该模型的有效性。重组尿激酶原似乎是与尿激酶一样有效的纤溶酶原激活剂（k2/Km = 0.05 μM-1 s-1），而尿激酶的k"2/K"m = 0.02 μM-1 s-1。这是由于以下事实：这种酶原对尿激酶的低分子量底物实际上无活性，但它与纤溶酶原形成米氏类型的中间体，其亲和力比活性酶与其底物的亲和力高得多。这在丝氨酸蛋白酶中是一种特殊现象。
