The cleavage and inactivation of plasminogen activator inhibitor type 1 and alpha 2-antiplasmin by reptilase, a thrombin-like venom enzyme

Reptilase, defibrase and ancrod are thrombin-like venom enzymes that cleave fibrinogen to release fibrinopeptide-A and generate fibrin monomers. Altho ugh these enzymes decrease fibrinogen levels in vivo, presumably by enhanci ng fibrinolytic activity, the mechanism has not been identified. In the pre sent study, we analyzed their effects on the inhibitors of fibrinolysis. Pl asminogen activator inhibitor-1 (PAI-1) was cleaved at its C-terminus by re ptilase and lost its specific activity. a2-Antiplasmin (a2-AP) was cleaved both at the Pro19-Leu20 peptide bond and at its C-terminus by reptilase, an d also lost its specific activity. The apparent second-order rate constants (mol/l per min per Batroxobin unit) were 0.22 for the cleavage of PAI-1 (3 .2 mu mol/l) and 0.19 for that of a2AP (6.4 mu mol/l), which were approxima tely 200-fold lower than that (47.0) for the cleavage of fibrinogen (1.1 mu mol/l). Neither defibrase nor ancrod cleaved and inactivated these inhibit ors. Only reptilase enhanced euglobulin clot lysis in vitro at high concent ration, due probably to PAI-1 inactivation. Since all these three enzymes e nhance fibrinolysis similarly during defibrination therapy, the neutralizat ion or inactivation of the inhibitors of fibrinolysis appeared not to repre sent the main mechanism for the enhancement, Blood Coag Fibrinol 11:145-153 (C) 2000 Lippincott Williams & Wilkins.