Thromb Haemost 2003; 89(01): 112-121
DOI: 10.1055/s-0037-1613550
Blood Coagulation, Fibrinolysis and Cellular Haemostasis
Schattauer GmbH

DX-9065a inhibition of factor Xa and the prothrombinase complex: mechanism of inhibition and comparison with therapeutic heparins

Alireza R. Rezaie
1   Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, Saint Louis, Missouri, USA
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Further Information

Publication History

Received 24 September 2002

Accepted after resubmission 24 October 2002

Publication Date:
09 December 2017 (online)

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Summary

Factor Xa (fXa) is the key enzyme of the prothrombinase complex that generates thrombin hence it is a good target for antithrombotic therapy. Here, the anti-fXa and anti-prothrombinase activities of DX-9065a which is an active-site directed inhibitor of fXa, and therapeutic heparins which are dependent on antithrombin (AT) for their anticoagulant function, were studied in amidolytic and proteolytic activity assays. It was found that DX-9065a is a competitive inhibitor of the Spectrozyme FXa (SpFXa) cleavage by both fXa and prothrom-binase with similar Ki values of ~10-20 nM. However, DX-9065a acted as a non-competitive inhibitor of prothrombin activation by prothrombinase with a Ki of ~26 nM. On the other hand, therapeutic heparins were effective catalysts of both fXa and prothrombinase inhibition by AT in the presence of SpFXa, but were ineffective in the presence of prothrombin. Further studies revealed that Tyr99, a residue in the extended S2-S4 binding pocket of fXa, plays a key role in determination of specificity of the DX-9065a interaction.