Wiman B, Boman L, Collen D
Eur J Biochem. 1978 Jun 1;87(1):143-6. doi: 10.1111/j.1432-1033.1978.tb12360.x.
The reaction between antiplasmin (A) and a low-molecular-weight form of plasmin (P) proceeds in at least two steps: a fast reversible second-order reaction followed by a slower irreversible first-order transition, and may be represented by: P +A k1 in equilibrium k-1 PA k2 leads to PA'. The low-Mr plasmin, which is obtained by limited elastase digestion, is composed of an intact B chain and a small A chain lacking the lysine-binding sites. The k1 of the reaction is (6.5 +/- 0.5) x 10(5) M-1 s-1 which is 30--60 times smaller than that for normal plasmin and antiplasmin. The dissociation constant of the first step is 1.9 x 10(-9) M which is 10 times higher than for normal plasmin and antiplasmin. The rate constant of the second step is (4.2 +/- 0.2) x 10(-3) s-1 for both normal and low-Mr plasmin. Low Mr plasmin which has substrate bound to its active site does not react or reacts only very slowly with antiplasmin. The reaction rate, however, is only slightly influenced by 6-aminohexanoic acid in concentrations up to 1 mM which decrease the reaction rate of normal plasmin approximately 50-fold. The findings further indicate that the lysine-binding site(s) of plasmin are of great importance for the rate of its reaction with antiplasmin.
抗纤溶酶（A）与低分子量形式的纤溶酶（P）之间的反应至少分两步进行：先是快速可逆的二级反应，接着是较慢的不可逆一级转变，其反应过程可用下式表示：P + A ⇌ k1 k - 1 PA → k2 PA'。通过有限的弹性蛋白酶消化获得的低分子量纤溶酶，由完整的B链和缺少赖氨酸结合位点的小A链组成。该反应的k1为(6.5 ± 0.5)×10⁵ M⁻¹ s⁻¹，比正常纤溶酶和抗纤溶酶的k1小30 - 60倍。第一步的解离常数为1.9×10⁻⁹ M，比正常纤溶酶和抗纤溶酶的解离常数高10倍。第二步的速率常数，正常纤溶酶和低分子量纤溶酶均为(4.2 ± 0.2)×10⁻³ s⁻¹。活性位点结合有底物的低分子量纤溶酶不与抗纤溶酶反应或反应非常缓慢。然而，浓度高达1 mM的6 - 氨基己酸对反应速率的影响很小，而同样浓度的6 - 氨基己酸可使正常纤溶酶的反应速率降低约50倍。这些发现进一步表明，纤溶酶的赖氨酸结合位点对其与抗纤溶酶的反应速率至关重要。
