Studies on Blood Coagulation Factor V

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Abstract
The interaction between stearates and coagulation factors consists of adsorption of the factors and partial activation resulting in thrombin formation. Factors V and XI are most readily adsorbed, closely followed by factor X. Activation is seen most clearly with low concentrations of the adsorbant. It can be inhibited by omission of Ca++ ions and addition of hirudin, thus it involves most probably the generation of thrombin. No thrombin is found in the reaction mixture due to the strong adsorption of thrombin on stearates. The effects of activation are small compared to the effect of adsorption time, pH, temperature and hirudin. Activity of factor V can be demonstrated in the adsorbed state but the factor cannot be eluted. Factor X shows no activity when adsorbed, but can be eluted from the powder. This suggests that the biological activity of factor V resides in a hydro-phylic part of the molecule, whereas the active centre of factor X probably is hidden but not destroyed by hydrophobic surfaces. The implications of these findings for the concept of prothrombinase formation on phospholipids are discussed.