Urano T, de Serrano V S, Gaffney P J, Castellino F J
Department of Chemistry, University of Notre Dame, Indiana 46556.
Arch Biochem Biophys. 1988 Jul;264(1):222-30. doi: 10.1016/0003-9861(88)90588-7.
The activation of human [Glu1]plasminogen ([Glu1]Pg) by single-chain human urokinase (SCUKase) displays a substantial lag phase at physiological levels of [Glu1]Pg. Employing a monoclonal antibody that exhibits a high level of specificity for SCUKase, as compared to two-chain urokinase (TCUKase), we have demonstrated conclusively that during this lag phase a progressive loss of SCUKase occurs, most likely resulting from its conversion to TCUKase, in a reaction catalyzed by plasmin (HPm). The overall activation of [Glu1]Pg by SCUKase is inhibited by physiological levels of Cl- and stimulated by epsilon-amino caproic acid. Kinetic studies demonstrate that both these effects are based on first, the reaction of [Glu1]Pg with the TCUKase that is formed during the activation, and, second, the concomitant rate at which HPm is provided for the conversion of SCUKase to TCUKase. The results indicate that at physiological levels of [Glu1]Pg, its activation in the presence of SCUKase is regulated in one manner by the rate at which SCUKase is converted to TCUKase, in a process that is strongly influenced by physiological levels of Cl-. Finally, and importantly, we show that SCUKase possesses very little, if any, inherent ability to activate [Glu1]Pg at a rate that influences the kinetics of HPm generation under physiological conditions of [Glu1]Pg and Cl- concentrations.
在生理水平的[Glu1]纤溶酶原（[Glu1]Pg）条件下，单链人尿激酶（SCUKase）对其激活呈现出显著的延迟期。与双链尿激酶（TCUKase）相比，我们使用了一种对SCUKase具有高度特异性的单克隆抗体，确凿地证明在这个延迟期内，SCUKase会逐渐丧失，最有可能是由于其在纤溶酶（HPm）催化的反应中转化为TCUKase所致。生理水平的Cl-会抑制SCUKase对[Glu1]Pg的整体激活，而ε-氨基己酸则会刺激该激活过程。动力学研究表明，这两种效应首先基于[Glu1]Pg与激活过程中形成的TCUKase的反应，其次基于为SCUKase转化为TCUKase提供HPm的伴随速率。结果表明，在生理水平的[Glu1]Pg条件下，其在SCUKase存在时的激活受到SCUKase转化为TCUKase速率的一种方式的调节，而这一过程受到生理水平的Cl-的强烈影响。最后且重要的是，我们表明在[Glu1]Pg和Cl-浓度的生理条件下，SCUKase几乎没有（如果有的话）以影响HPm生成动力学的速率激活[Glu1]Pg的内在能力。
