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Intrinsic versus extrinsic coagulation. Kinetic considerations.

B J Warn-Cramer, S P Bajaj

    The Biochemical Journal
    |November 1, 1986
    PubMed
    Summary

    Both Factor XIa and Factor VIIa activate Factor IX, with distinct kinetics. This study reveals their significant physiological roles in blood coagulation, impacting hemostasis.

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    Area of Science:

    • Biochemistry
    • Hematology
    • Molecular Biology

    Background:

    • Factor IX activation is a critical step in the intrinsic coagulation pathway.
    • Factor VIIa, in complex with tissue factor, initiates the extrinsic pathway.
    • Understanding the comparative kinetics of Factor IX activation is crucial for hemostasis research.

    Purpose of the Study:

    • To compare the kinetics of Factor IX activation by Factor XIa/Ca2+ versus Factor VIIa/tissue factor/Ca2+.
    • To elucidate the physiological significance of both Factor XIa and Factor VIIa in Factor IX activation.

    Main Methods:

    • Utilized purified human proteins and tritiated-activation-peptide-release assays.
    • Employed detergent-extracted brain tissue factor and U937 cells as sources of tissue factor.
    • Measured kinetic constants (Km, kcat) for enzyme-substrate interactions.

    Main Results:

    • Kinetic constants for Factor XIa activation of Factor IX: Km = 310 nM, kcat = 25 min-1.
    • Kinetic constants for Factor VIIa activation of Factor IX: Km = 210 nM, kcat = 15 min-1.
    • Factor VIIa/tissue factor demonstrated efficient activation of Factor X (Km = 205 nM, kcat = 70 min-1).

    Conclusions:

    • Both Factor XIa and Factor VIIa exhibit significant roles in Factor IX activation.
    • Kinetic data support the physiological relevance of these distinct activation pathways.
    • High-molecular-weight kininogen did not influence Factor IX activation rates under tested conditions.

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