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Journal of Biochemistry Advance Access originally published online on October 30, 2008
Journal of Biochemistry 2009 145(1):123-128; doi:10.1093/jb/mvn145
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© The Authors 2008. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved

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

Midori Ishikawa1, Makoto Kumashiro1, Yasuo Yamazaki, Hideko Atoda and Takashi Morita*

Department of Biochemistry, Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose, Tokyo 204-8588, Japan

*To whom correspondence should be addressed. Tel/Fax: +81-42-495-8479, E-mail: tmorita{at}my-pharm.ac.jp

Received September 25, 2008; Accepted October 25, 2008


  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 kcat of thrombin formation through inhibition of interaction between factor Xa and factor Va. IX/X-bp also inhibited the decrease of Km 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.

Key Words: anticoagulant protein, coagulation factor IX, factor X, IX/X-bp, prothrombinase

Abbreviations: IX/X-bp, blood coagulation factor IX/factor X-binding protein isolated from the venom of T. flavoviridis; IX-bp, factor IX-binding protein; EGF, Epidermal growth factor; Gla, {gamma}-carboxyglutamic acid

1These authors are equally contributed to this work.


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