Lijnen H R, Van Hoef B, De Cock F, Okada K, Ueshima S, Matsuo O, Collen D
Center for Thrombosis and Vascular Research, University of Leuven, Belgium.
J Biol Chem. 1991 Jun 25;266(18):11826-32.
The mechanism of plasminogen activation by recombinant staphylokinase was studied both in the absence and in the presence of fibrin, in purified systems, and in human plasma. Staphylokinase, like streptokinase, forms a stoichiometric complex with plasminogen that activates plasminogen following Michaelis-Menten kinetics with Km = 7.0 microM and k2 = 1.5 s-1. In purified systems, alpha 2-antiplasmin inhibits the plasminogen-staphylokinase complex with k1(app) = 2.7 +/- 0.30 x 10(6) M-1 s-1 (mean +/- S.D., n = 12), but not the plasminogen-streptokinase complex. Addition of 6-aminohexanoic acid induces a concentration-dependent reduction of k1(app) to 2.0 +/- 0.17 x 10(4) M-1 s-1 (mean +/- S.D., n = 5) at concentrations greater than or equal to 30 mM, with a 50% reduction at a 6-aminohexanoic acid concentration of 60 microM. Staphylokinase does not bind to fibrin, and fibrin stimulates the initial rate of plasminogen activation by staphylokinase only 4-fold. Staphylokinase induces a dose-dependent lysis of a 0.12-ml 125I-fibrin-labeled human plasma clot submersed in 0.5 ml of citrated human plasma; 50% lysis in 2 h is obtained with 17 nM staphylokinase and is associated with only 5% plasma fibrinogen degradation. Corresponding values for streptokinase are 68 nM and more than 90% fibrinogen degradation. In the absence of a fibrin clot, 50% fibrinogen degradation in human plasma in 2 h requires 790 nM staphylokinase, but only 4.4 nM streptokinase. These results suggest the following mechanism for relatively fibrin-specific clot lysis with staphylokinase in a plasma milieu. In plasma in the absence of fibrin, the plasminogen-staphylokinase complex is rapidly neutralized by alpha 2-antiplasmin, thus preventing systemic plasminogen activation. In the presence of fibrin, the lysine-binding sites of the plasminogen-staphylokinase complex are occupied and inhibition by alpha 2-antiplasmin is retarded, thus allowing preferential plasminogen activation at the fibrin surface.
在纯化系统以及人血浆中，研究了有无纤维蛋白存在时重组葡萄球菌激酶激活纤溶酶原的机制。与链激酶一样，葡萄球菌激酶与纤溶酶原形成化学计量复合物，该复合物按照米氏动力学激活纤溶酶原，Km = 7.0微摩尔，k2 = 1.5秒-1。在纯化系统中，α2 -抗纤溶酶抑制纤溶酶原 - 葡萄球菌激酶复合物，k1（app）= 2.7±0.30×106 M-1秒-1（平均值±标准差，n = 12），但不抑制纤溶酶原 - 链激酶复合物。添加6 -氨基己酸会导致k1（app）在浓度大于或等于30毫摩尔时呈浓度依赖性降低至2.0±0.17×104 M-1秒-1（平均值±标准差，n = 5），在6 -氨基己酸浓度为60微摩尔时降低50%。葡萄球菌激酶不与纤维蛋白结合，纤维蛋白仅将葡萄球菌激酶激活纤溶酶原的初始速率提高4倍。葡萄球菌激酶能诱导溶解于0.5毫升枸橼酸化人血浆中的0.12毫升125I -纤维蛋白标记的人血浆凝块，呈剂量依赖性；17纳摩尔葡萄球菌激酶在2小时内可实现50%溶解，且仅伴有5%的血浆纤维蛋白原降解。链激酶的相应值分别为68纳摩尔和超过90%的纤维蛋白原降解。在无纤维蛋白凝块的情况下，人血浆中2小时内50%的纤维蛋白原降解需要790纳摩尔葡萄球菌激酶，但仅需4.4纳摩尔链激酶。这些结果提示了在血浆环境中葡萄球菌激酶相对纤维蛋白特异性凝块溶解的如下机制。在无纤维蛋白的血浆中，纤溶酶原 - 葡萄球菌激酶复合物会迅速被α2 -抗纤溶酶中和，从而防止全身性纤溶酶原激活。在有纤维蛋白存在时，纤溶酶原 - 葡萄球菌激酶复合物的赖氨酸结合位点被占据，α2 -抗纤溶酶的抑制作用受阻，从而允许在纤维蛋白表面优先激活纤溶酶原。
