Effects of α2-Plasmin Inhibitor on Fibrin Clot Lysis. Its Comparison with α2-Macroglobulin

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Abstract
The major plasmin inhibitors namely α2-plasmin inhibitor and α2-macroglobulin were compared for their effects on lysis of fibrin clot. Plasmin fibrinolytic activity was immediately inhibited by α2-plasmin inhibitor, whereas α2-macroglobulin inhibited plasmin progressively. Urokinase(plasminogen activator)-induced clot lysis was inhibited efficiently by α2-plasmin inhibitor present in the clot. Inhibition of urokinase-induced clot lysis by α2-macroglobulin was weak and the molar concentration necessary for α2-macroglobulin to achieve the same degree of inhibition as that achieved with α2-plasmin inhibitor was about 10 times higher than that of α2-plasmin inhibitor. Binding of Lys-plasminogen to fibrin was inhibited by α2-plasmin inhibitor but not by α2-macroglobulin. Molar concentrations of α2-plasmin inhibitor which were effective in inhibiting the binding were 30 times less than that of 6-aminohexanoic acid. α2-Plasmin inhibitor was found to interact with Lys-plasminogen to form a weakly-bound complex which is dissociable in the presence of 6-aminohexanoic acid, suggesting that inhibition of binding of Lys-plasminogen to fibrin by α2-plasmin inhibitor may be due to interaction of α2-plasmin inhibitor with a specific site of the plasminogen molecule and that the site may be 6-aminohexanoic acid-binding site. It is suggested that α2-plasmin inhibitor is more reactive and efficient inhibitor of fibrinolysis than α2-macroglobulin.