Anticoagulant Mechanism of Factor IX/factor X-binding Protein Isolated from the Venom of Trimeresurus flavoviridis

Authors: Ishikawa, Midori; Kumashiro, Makoto; Yamazaki, Yasuo; Atoda, Hideko; Morita, Takashi

Source: The Journal of Biochemistry, Volume 145, Number 1, 30 January 2009 , pp. 123-128(6)

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Abstract:

Anticoagulant mechanism of the coagulation factor IX/factor X-binding protein (IX/X-bp) isolated from the venom of Trimeresurus flavoviridis was investigated. IX/X-bp had no effect on the amidase activity of factor Xa measured with a synthetic peptide substrate Boc-Leu-Gly-Arg-pNA. Prothrombin activation by factor Xa without cofactors, such as factor Va and phospholipids, was only slightly influenced by IX/X-bp. However, prothrombin activation by factor Xa in the presence of factor Va resulted in IX/X-bp inhibiting the increase of k_cat of thrombin formation through inhibition of interaction between factor Xa and factor Va. IX/X-bp also inhibited the decrease of k_m for thrombin formation through interaction with phospholipids. Thus, IX/X-bp appears to act as an anticoagulant protein by inhibiting the interaction between factor Xa and its cofactors in the prothrombinase complex by binding to the Gla domain of factor Xa.

Keywords: anticoagulant protein; coagulation factor IX; factor X; IX/X-bp; prothrombinase

Document Type: Regular paper

DOI: http://dx.doi.org/10.1093/jb/mvn145

Publication date: 2009-01-30