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Prothrombin activation on dioleoylphosphatidylcholine membranes
J W Govers-Riemslag1, M P Janssen, R F Zwaal
1Department of Biochemistry, University of Limburg, Maastricht, The Netherlands.
European Journal of Biochemistry
|February 15, 1994
Summary
Neutral phosphatidylcholine membranes significantly accelerate prothrombin activation, especially with unsaturated fatty acids, factor Va, and calcium ions. This interaction is crucial for prothrombinase complex assembly, even without anionic phospholipids.
Area of Science:
- Biochemistry
- Membrane Biophysics
- Hemostasis
Background:
- Factor Xa-catalyzed prothrombin activation is typically enhanced by negatively charged phospholipids and calcium ions.
- Previous research indicated that neutral phosphatidylcholine membranes could also stimulate prothrombin activation.
Purpose of the Study:
- To conduct a detailed analysis of the prothrombin-converting activity of phosphatidylcholine membranes.
- To investigate the role of phosphatidylcholine in prothrombinase complex formation and activity.
Main Methods:
- Utilized dioleoylphosphatidylcholine [(Ole)2GroPCho] membranes to study prothrombin activation.
- Performed thin-layer chromatography to assess phospholipid composition.
- Measured kinetic parameters including Km, Vmax, and Kd for factor XaVa complex formation at varying ionic strengths.
Main Results:
- Phosphatidylcholine membranes, particularly those with unsaturated side chains, significantly stimulated prothrombin activation in the presence of factor Va, calcium ions, and at low ionic strength.
- The prothrombinase activity was not due to anionic phospholipid contamination, as (Ole)2GroPCho contained <0.1% anionic lipids.
- (Ole)2GroPCho membranes accelerated prothrombin activation approximately 100-fold under optimal conditions (low ionic strength, factor Va, Ca2+).
- Increased ionic strength significantly reduced prothrombin activation by increasing the dissociation constant (Kd) for factor XaVa complex formation.
Conclusions:
- Neutral phosphatidylcholine membranes can effectively support prothrombinase activity, similar to anionic phospholipids.
- The interaction of prothrombin and factor Va with phosphatidylcholine membranes is dependent on calcium ions and gamma-carboxyglutamic acid domains.
- These findings suggest conserved mechanisms for prothrombinase complex assembly on both neutral and anionic lipid surfaces.