Norrman B, Wallén P, Rånby M
Eur J Biochem. 1985 May 15;149(1):193-200. doi: 10.1111/j.1432-1033.1985.tb08911.x.
The rate of 'Glu'-plasminogen activation by tissue plasminogen activator was repeatedly determined during a fibrinolytic process. The process was found to proceed via two distinct phases. The kinetics of each phase obeyed Michaelis-Menten equation: First phase; kcat about 0.17 s-1 and Km about 1 microM, second phase; kcat about 0.13 s-1 and Km about 0.06 microM. Practically identical results were obtained with one-chain as with two-chain tissue plasminogen activator. Transition from first to second phase occurred when the system had been exposed to a certain degree of plasmin digestion. Electrophoretic analysis demonstrated time correlation between the appearance of minimally degraded fibrin (X-fragments) and the transition. No such correlation was found between transition and conversion of 'Glu'-plasminogen to 'Lys'-plasminogen. The effect can result in an acceleration (up to 13-fold) of the fibrinolytic process once a slight degradation of the fibrin has taken place. In vivo, the effect described may constitute a mechanism that protects a fibrin clot from premature lysis.
在纤维蛋白溶解过程中，反复测定组织型纤溶酶原激活物对“Glu”-纤溶酶原的激活率。发现该过程通过两个不同阶段进行。每个阶段的动力学均符合米氏方程：第一阶段，催化常数（kcat）约为0.17 s-1，米氏常数（Km）约为1 μM；第二阶段，kcat约为0.13 s-1，Km约为0.06 μM。单链组织型纤溶酶原激活物和双链组织型纤溶酶原激活物得到的结果几乎相同。当系统受到一定程度的纤溶酶消化时，会发生从第一阶段到第二阶段的转变。电泳分析表明，最小降解纤维蛋白（X片段）的出现与转变之间存在时间相关性。在转变与“Glu”-纤溶酶原向“Lys”-纤溶酶原的转化之间未发现此类相关性。一旦纤维蛋白发生轻微降解，该效应可导致纤维蛋白溶解过程加速（高达13倍）。在体内，所述效应可能构成一种保护纤维蛋白凝块免于过早溶解的机制。
