Protein S is required for specific activated protein C binding to the bovine platelet surface (Kd = 11 +/- 3 nM) and subsequent rapid factor Va inactivation.
Protein S is essential for activated protein C to bind to platelet surfaces and rapidly inactivate factor Va, a key mechanism in the anticoagulant pathway.
Gel-filtered platelets accelerate activated protein C inactivation of factor Va in a reaction that requires the presence of protein S. With protein S present, specific activated protein C binding to the platelet surface is observed (Kd = 11 +/- 3 nM, 203 +/- 20 sites/platelet). The concentration dependence of the activated protein C-mediated factor Va inactivation is in close agreement with the binding. The observed binding is specific since protein C does not compete with activated protein C. Platelet-bound activated protein C is approximately 8000 times more active than the solution-phase enzyme. Platelet activation with thrombin results in formation of a site capable of accelerating factor Va inactivation by activated protein C in the absence of added protein S. This cell surface site is blocked by the addition of affinity purified antibodies to protein S. We conclude that protein S is required for activated protein C binding to the platelet surface and subsequent rapid factor Va inactivation. Platelet activation leads to the expression of either protein S or an antigenically related protein which can substitute for exogenously added protein S.
Harris et al. (Fri,) reported a other. Protein S vs. Absence of protein S was evaluated on Activated protein C binding and factor Va inactivation. Protein S is required for specific activated protein C binding to the bovine platelet surface (Kd = 11 +/- 3 nM) and subsequent rapid factor Va inactivation.