Effects of Human Granulocyte Elastase on Fibrinolysis

Abstract

The specific limited proteolysis of human plasminogen by human granulocyte elastase results in the cleavage of three peptides from the heavy chain of plasminogen. These three peptides bind to lysine- and fibrin-Sepharose. The remainder of the molecule possesses a molecular weight of 38000 and represents a fully activatable plasminogen lacking the lysine binding site (s) in the heavy chain. Upon treatment of this low molecular weight form of plasminogen with urokinase, esterolytic, fibrinolytic and amidolytic activities appear. The low molecular weight form of plasmin consists of two disulfide-linked polypeptide chains with molecular weights of approximately 25000 and 13000. The kinetic parameters of hydrolysis of synthetic substrates by the low molecular weight form of plasmin and native plasmin, respectively, are similar. Furthermore, the inhibitions of the two enzymes by several inhibitors of the hydrolysis of Blue Dextran-fixed fibrin are identical. The initial rate of activation with urokinase is about two times faster for the low molecular weight form of plasminogen than for native plasminogen, and the activation of native plasminogen by urokinase is inhibited by plasma α₂-antiplasmin, whereas the activation of the low molecular weight form of plasminogen is not. Urokinase-induced clot lysis is inhibited efficiently by α₂-antiplasmin, but the inhibitory effect of α₂-antiplasmin is removed by heavy chain fragments containing lysine binding site (s), which are obtainable from plasminogen by limited elastase digestion. Urokinaseinduced fibrinolytic activity of plasma is promoted by human granulocyte elastase in an apparently time-dependent manner. The findings further indicate that the lysine binding site (s) in the heavy chain of plasmin (ogen) are of great importance in relation to the rate of its reaction with α₂-antiplasmin.