Protein C is a vitamin K-dependent serine protease that is produced in the liver and made up of 2 polypeptide chains. The 62 kDa proenzyme is activated by thrombin bound to an endothelial surface receptor and the active enzyme cleaves factor Va and VIIIa inhibiting blood coagulation. The molecular weight of the active enzyme is 55 kDa and the normal concentration in human plasma is approximately 1-3 ng/ml while the concentration of the proenzyme is approximately 3 ug/mL due to the very fast turnover.
