Kowalska-Loth B, Zakrzewski K
Acta Biochim Pol. 1975;22(4):327-39.
The activation of human plasminogen by a highly purified staphylokinase was investigated using casein or an active site titrant (p-nitrophenyl-p-guanidinobenzoate, NPGB) as a substrate. The reaction rate was time dependent, showing a pronounced lag period with either substrate. Saturation curve estimated from the caseinolytic assay was sigmoid, but changed to quasi-hyperbolic in the presence of pre-formed human plasmin. With NPGB, the extent of plasminogen conversion into esterolytic plasmin was directly proportional to staphylokinase concentration, and the saturation point was reached when the molar concentration of staphylokinase equaled that of plasminogen. It is concluded that staphylokinase acts stoichiometrically, forms an equimolar complex with plasminogen, and thus is not an enzyme but a modifier. Staphylokinase-activated plasminogen exhibits properties of a hysteretic enzyme.
使用酪蛋白或活性位点滴定剂（对硝基苯基-对胍基苯甲酸酯，NPGB）作为底物，研究了高纯度葡萄球菌激酶对人纤溶酶原的激活作用。反应速率与时间相关，两种底物均显示出明显的延迟期。酪蛋白溶解试验估计的饱和曲线呈S形，但在预先形成的人纤溶酶存在下变为准双曲线。对于NPGB，纤溶酶原转化为酯解性纤溶酶的程度与葡萄球菌激酶浓度成正比，当葡萄球菌激酶的摩尔浓度等于纤溶酶原的摩尔浓度时达到饱和点。得出的结论是，葡萄球菌激酶按化学计量起作用，与纤溶酶原形成等摩尔复合物，因此不是一种酶而是一种修饰剂。葡萄球菌激酶激活的纤溶酶原表现出滞后酶的特性。
