Propriedades anticoagulantes de duas metaloproteinases, mutalisina I e mutalisina II, isoladas do veneno da serpente Lachesis muta muta

Abstract

Two hemorrhagic factors, mutalysin I and II (LHF-I and LHF-II) were isolated from bushmaster snake (Lachesis muta muta) venom by gel filtration and ion exchange chromatography. The purified proteins represent 12 and 1% respectively of the hemorrhagic activity in the whole venom. The mutalysins were characterized as metalloendopeptidases and contain zinc and calcium. LHF-I (100 kDa, two subunits) and LHF-II (22,4 kDa, single chain) hydrolyze the Aa > Bb of fibrinogen without clot formation. The specific fibrinogenolytic activity was estimated as 25.5 and 13 mg of fibrinogen/min/mg protein for LHF-II and LHF-I respectively. In vitro, the mutalysins showed direct fibrinolytic activity. Analysis by SDS-PAGE of fibrin hydrolysis by both metalloenzymes showedthat LHF-II (0.22 mM) digested completely the a, b and g chains. On the other hand, LHF-I (0.56 mM) hydrolyzes selectively the a chain of fibrin, leaving the b and g chains unaffected. The mutalysins I and II are fibrinogenases which induce hemorrhage without clot formation. In contrast with the plasminogen activator - based thrombolytic agents such as streptokinase, LHF-I and LHF-II do not activate plasminogen. Mutalysin II has no effect on protein C activation and does not inhibit platelet aggregation in human PRP stimulated by ADP or collagen. In addition to hemorrhagic effect by direct proteolysis on capillarywalls, the hemorrhagic toxins can digest other protein components of thehaemostatic system and also activate endogenous proteinases.