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Coagulation factor IXa binding to activated platelets and platelet-derived microparticles: a flow cytometric study
M Hoffman1, D M Monroe, H R Roberts
1Department of Pathology, University of North Carolina, Chapel Hill.
Thrombosis and Haemostasis
|July 6, 1992
Summary
Activated factor IX (IXa) binds to activated platelets and microparticles via two calcium-dependent sites, one high-affinity and one low-affinity, revealing new insights into blood coagulation.
Area of Science:
- Hematology
- Biochemistry
- Molecular Biology
Background:
- Factor IX is crucial for blood coagulation, participating in both intrinsic and extrinsic pathways.
- Activated factor IX (IXa) forms a complex with factor VIIIa on platelet surfaces to activate factor X.
- Understanding IXa interactions with platelets is key to elucidating coagulation mechanisms.
Purpose of the Study:
- To investigate the binding characteristics of factor IXa to thrombin-activated platelets without factor VIIIa.
- To identify and quantify factor IXa binding sites on platelets and associated microparticles.
Main Methods:
- Flow cytometry was employed to analyze factor IXa binding to activated platelets.
- Indirect immunofluorescence staining detected platelet-bound IXa and GPIb.
- Microparticles were identified by light scattering properties.
Main Results:
- Two distinct binding sites for factor IXa on activated platelets were identified.
- A high-affinity site (Kd = 1.6 nM) and a low-affinity site (Kd ≈ 100 nM) were characterized.
- Binding to both sites was calcium-dependent.
Conclusions:
- Factor IXa exhibits both high-affinity and calcium-dependent low-affinity binding to activated platelets and microparticles.
- These findings contribute to understanding the role of platelets in factor IXa-mediated coagulation.
- The distribution of binding sites on microparticles versus platelet proteins warrants further investigation.