The binding of the anticoagulation factor I from the venom Agkistrodon acutus to activated factor X

Anticoagulation factor I (ACF I) from the venom of Agkistrodon acutus prolo nged plasma prothrombin time (PPT) with dose-dependent manner and exhibited marked anticoagulant activity only at the concentration higher than its cr itical concentration (12 nmol/L). it was discovered that ACF I formed a 1 : 1 complex with activated coagulation factor(FXa] in the presence of Ca2+ io ns by the method of polyacrylamide gel electrophoresis. Both native ACF I a nd decalcified ACF failed to form complexes with FXa in the absence of Ca2. Sr2+ ions were able to replace Ca2+ ions in the binding of ACF I to FXa, but both Ba2+ ions and Tb3+ ions were ineffective. ACF I was a new member o f the IX/X-bp family in the C-type lectin superfamily, and had a amino acid composition similar to the other members of this family It was composed of 251 amino acid residues with a molecular weight of 29 603.6 u on non-reduc ing condition, determined by MALDI-TOF-MS, and a molecular weight of 14.7 k u on reducing condition, determined by the sodium dodecyl sulfate-polyacryl amide gel electrophoresis (SDS-PAGE).