Protein C

Protein C is an endogenously occurring plasma protein that plays a key role within the coagulation cascade. Also known as blood coagulation factor XIV, Protein C is a zymogen, or enzyme precursor, of a vitamin K-dependent anticoagulant glycoprotein (serine protease) that is synthesized in the liver. It is converted by the thrombin/thrombomodulin-complex on the endothelial cell surface to Activated Protein C (APC). Once in its activated form, APC functions as a serine protease with potent anticoagulant effects, especially in the presence of its cofactor protein S. APC exerts its effect by inactivating essential components of the coagulation cascade (specifically factors V and VIII), which leads to a decrease in thrombin formation, and therefore a reduction in clot formation.