title: Anticoagulant mechanism of factor IX/factor X-binding protein isolated from the venom of Trimeresurus flavoviridis.
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.
authors.affiliation: Department of Biochemistry, Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose, Tokyo 204-8588, Japan.
authors.forename: Midori
authors.initials: M
authors.lastname: Ishikawa
authors.forename: Makoto
authors.initials: M
authors.lastname: Kumashiro
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Yamazaki
authors.forename: Hideko
authors.initials: H
authors.lastname: Atoda
authors.forename: Takashi
authors.initials: T
authors.lastname: Morita
mesh_terms: D000818:Animals; D001665:Binding Sites; D003435:Crotalid Venoms / Q000737:chemistry* / Q000378:metabolism; D005164:Factor IX / Q000378:metabolism*; D005170:Factor X / Q000378:metabolism*; D007700:Kinetics; D011516:Prothrombin / Q000378:metabolism; D030162:Reptilian Proteins / Q000737:chemistry* / Q000378:metabolism; D017841:Trimeresurus / Q000378:metabolism*
chemical_list: D003435:Crotalid Venoms; D030162:Reptilian Proteins; C109516:factor IX-binding protein, Trimeresurus flavoviridis; D011516:Prothrombin; D005164:Factor IX; D005170:Factor X