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Related Experiment Videos

Zymogen factor IX potentiates factor IXa-catalyzed factor X activation.

F S London1, P N Walsh

  • 1Department of Biochemistry, The Sol Sherry Thrombosis Research Center Temple University School of Medicine, 3400 North Broad Street, Philadelphia, Pennsylvania 19140, USA.

Biochemistry
|August 10, 2000
PubMed
Summary

Physiologic levels of zymogen factor IX enhance the intrinsic pathway of blood coagulation. This occurs by increasing the affinity of factor IXa for the factor X activation complex on activated platelets and lipid surfaces.

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Binding studies of the enzyme (factor IXa) with the cofactor (factor VIIIa) in the assembly of factor-X activating complex on the activated platelet surface.

Journal of thrombosis and haemostasis : JTH·2003

Area of Science:

  • Hematology
  • Biochemistry
  • Molecular Biology

Background:

  • The intrinsic pathway of blood coagulation involves a cascade of enzymatic activation steps.
  • Factor X activation is a crucial step, significantly accelerated by the tenase complex on activated platelet surfaces.
  • The role of zymogen factor IX at physiological concentrations in this process requires further elucidation.

Purpose of the Study:

  • To investigate the effect of physiological concentrations of zymogen factor IX on factor X activation.
  • To determine if factor IX influences the affinity of factor IXa for the intrinsic tenase complex.
  • To assess the specificity of this effect for factor IX.

Main Methods:

  • Utilized activated platelets and negatively charged phospholipid vesicles as surfaces for factor X activation assays.

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  • Measured the binding affinity (Kd,app) of factor IXa in the presence and absence of factor IX and factor VIIIa.
  • Employed radiolabeled factor IX and factor X with PAGE analysis to assess reaction kinetics and rule out feedback mechanisms.

    • Main Results:

    • Physiological concentrations of factor IX (approximately 100 nM) potentiated factor IXa-catalyzed factor X activation on both activated platelets and lipid vesicles.
    • Factor IX significantly reduced the apparent dissociation constant (Kd,app) of factor IXa, indicating increased affinity for the activation complex.
    • The observed potentiation was specific to factor IX and not observed with other vitamin K-dependent proteins, and was independent of factor Xa-mediated feedback.

    Conclusions:

    • Zymogen factor IX, at physiological plasma concentrations, specifically enhances the intrinsic pathway of coagulation.
    • Factor IX increases the affinity of factor IXa for the tenase complex, thereby promoting efficient factor X activation.
    • These findings highlight a critical regulatory role for factor IX in hemostasis under normal physiological conditions.