Urano T, Chibber B A, Castellino F J
Proc Natl Acad Sci U S A. 1987 Jun;84(12):4031-4. doi: 10.1073/pnas.84.12.4031.
The activation of human [Glu1]plasminogen [( Glu1]Pg) by high-molecular-weight two-chain human urinary urokinase [EC 3.4.21.31) and low-molecular-weight two-chain human urinary urokinase is inhibited by Cl- at physiological concentrations and stimulated by epsilon-aminohexanoic acid (epsilon Ahx; epsilon-aminocaproic acid). The inhibition by Cl- does not occur in the presence of concentrations of epsilon Ahx that saturate the acid's weak binding sites on [Glu1]Pg, and the stimulation by epsilon Ahx is maximally exhibited in the presence of Cl-. We have used intrinsic fluorescence measurements with [Glu1]Pg to show that the conformational alteration and the concomitant increase in activation rate that accompanies epsilon Ahx-binding to [Glu1]Pg in the presence of Cl- does not occur in the same manner without Cl-. Further, the decrease in the intrinsic fluorescence that is attendant to Cl- binding to [Glu1]Pg in the absence of epsilon Ahx is not observed in the presence of this effector molecule. Analyses of the results of this manuscript strongly indicate that a conformation of [Glu1]Pg that is not optimal for its activation by urokinase is adopted in the presence of Cl-, and this is relieved by epsilon Ahx. This has important implications in the inhibition of [Glu1]Pg activation in the solution phase of blood plasma and in the large acceleration of this process when plasminogen is bound to physiological positive effectors via its epsilon Ahx-binding site(s).
在生理浓度下，氯离子（Cl⁻）可抑制高分子量双链人尿激酶[EC 3.4.21.31]和低分子量双链人尿激酶对人[Glu1]纤溶酶原[（Glu1）Pg]的激活作用，而ε-氨基己酸（εAhx；ε-氨基己酸）则可刺激该激活过程。在存在饱和[Glu1]Pg上酸性弱结合位点的εAhx浓度时，Cl⁻的抑制作用不会发生，并且εAhx的刺激作用在有Cl⁻存在时表现得最为明显。我们利用[Glu1]Pg的固有荧光测量结果表明，在有Cl⁻存在的情况下，εAhx与[Glu1]Pg结合时伴随的构象改变和激活速率的相应增加，在没有Cl⁻时不会以相同方式发生。此外，在没有εAhx时伴随Cl⁻与[Glu1]Pg结合的固有荧光降低，在有这种效应分子存在时未被观察到。对本手稿结果的分析强烈表明，在有Cl⁻存在时，[Glu1]Pg会采用一种对其被尿激酶激活而言并非最佳的构象，而εAhx可缓解这种构象。这对于抑制血浆溶液相中[Glu1]Pg的激活以及当纤溶酶原通过其εAhx结合位点与生理正效应物结合时该过程的大幅加速具有重要意义。
