What is the role of protein C and S in the etiology of nonplatelet hemostatic disorders?

Updated: Oct 06, 2020
  • Author: Irene S Pakos, DO; Chief Editor: Perumal Thiagarajan, MD  more...
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Protein C and S are vitamin K–dependent factors that participate in the thrombomodulin–protein C system. Thrombomodulin and thrombin form a complex on the endothelial cell plasma membrane in response to injury, with activated protein S serving as a cofactor. This complex attracts and binds protein C in the presence of calcium ion to produce activated protein C (aPC). aPC inactivates factors Va and VIIIa, thus halting the coagulation cascade. It also neutralizes plasminogen-activator inhibitor I, thereby facilitating fibrinolysis. Deficiency of the naturally occurring anticoagulant proteins antithrombin III, protein C, and protein S, in addition to aPCR due to the factor V Leiden gene mutation, are associated with inherited thrombophilia.

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