A Novel Blood Coagulation Factor IX/Factor X-Binding Protein with Anticoagulant Activity from the Venom of Trimeresurus flavoviridis(Habu Snake): Isolation and Characterization1

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Abstract
Using affinity chromatography on a column of factor X-Cellulofine, we have isolated a novel blood coagulation factor X-binding protein with anticoagulant activity from the venom of Trimeresurus flavoviridis (Habu snake). This anticoagulant protein was also purified by chromatography on Sephadex G-75 and S-Sepharose Fast Flow. The yield of the purified protein was approximately 16 mg from 400 mg of crude venom. The purified protein gave a single band on both analytical alkaline disc-gel electrophoresis and SDS-PAGE. This protein had a relative molecular weight (Mr) after SDS-PAGE of 27, 000 before reduction of disulfide bonds and 14, 000 after reduction of disulfide bonds. The protein prolonged the clotting time induced by kaolin or factor Xa. In the presence of Ca2+, it formed a complex with factor X, the molar ratio being 1 to 1. Similar complex formation was observed with factor Xa and factor IX/factor IXa, but not with other vitamin K-dependent coagulation factors, Le., prothrombin, factor VII, protein C, protein S, and protein Z. The interaction of this anticoagulant protein with factor IX/factor X was dependent on γ-carboxyglutamic acid (Gla) domains, since Gla-domainless derivatives of factor X and factor IXαβ' did not interact with this anticoagulant protein.