Effects of thrombomodulin and coagulation Factor Va-light chain on protein C activation in vitro.
Protein C activation by thrombin is significantly accelerated by the endothelial cell surface protein thrombomodulin, Factor Va, or its light chain. In this study we have compared the activation of protein C in the presence of either cofactor and examined the possibility that thrombomodulin and Factor Va-light chain act together to regulate protein C activation by thrombin. At all concentrations of protein C used, thrombomodulin was 20 times more efficient than Factor Va-light chain in accelerating protein C activation by thrombin. Protein C treated with chymotrypsin to remove the amino-terminal 41 amino acids that contain the gamma-carboxyglutamyl residues was activated by the thrombin-thrombomodulin complex at an identical rate to native protein C, whereas the modified protein C was activated by Factor Va-light chain and thrombin at only 5% of the rate obtained by using native protein C. Increasing concentrations of Factor Va-light chain, greater than or equal to 30 nM, inhibited thrombin-thrombomodulin catalyzed protein C activation with complete inhibition observed at 90 nM Factor Va-light chain. On the other hand, increasing thrombomodulin concentrations did not inhibit protein C activation by Factor Va-light chain and thrombin. These reactions in solution mimic, in part, those obtained on endothelial cells where protein C lacking the gamma-carboxyglutamyl domain is activated poorly and Factor Va-light chain at concentrations greater than 50 nM inhibited the activation of native protein C. The results of this study suggest that thrombomodulin and Factor Va-light chain may act in concert to regulate protein C activation by thrombin.
D000818:Animals; D001667:Binding, Competitive; D002417:Cattle; D004789:Enzyme Activation; D005165:Factor V / Q000502:physiology*; D015943:Factor Va; D006023:Glycoproteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D010446:Peptide Fragments / Q000502:physiology*; D011486:Protein C; D011817:Rabbits; D011956:Receptors, Cell Surface / Q000502:physiology*; D018179:Receptors, Thrombin; D013917:Thrombin / Q000378:metabolism
D006023:Glycoproteins; D010446:Peptide Fragments; D011486:Protein C; D011956:Receptors, Cell Surface; D018179:Receptors, Thrombin; D015943:Factor Va; D005165:Factor V; D013917:Thrombin