Protein C and S in Swiss Blood Donors

Protein C, which is produced by the liver, is a vitamin K-dependent two-chain glycoprotein with a molecular weight of 62 kd [1]. It has a short half-life of six hours [2,3] and is found in plasma in an inactive form with a concentration of 4.8 ±1.0 µg/ml. Activated protein C is a potent inhibitor of factors Va and VIIIa; in this way it functions as a regulator of coagulation. In addition, protein C stimulates fibrinolysis by inhibiting plasminogen activator-inhibitor (PAI). Protein S is also synthesized by the liver and vitamin K-dependent. It has no enzymatic activity by itself, but enhances as a cofactor protein C activity by forming a complex which promotes the inhibition of factors Va and VIIIa. Approximately 40% of circulating protein S is in the free form; the rest is inactive, being bound to the C4b-binding protein.