Coagulation Factor XIV / Protein C is a vitamin K-dependent serine protease synthesized in liver as a single-chain precursor. Present in plasma at 3 to 5 mg/L, protein C plays a key role in anticoagulation. Physiologically, the inactive forms of protein C are converted to the active form by thrombin, which releases the activation peptide. The active protein C cleaves factor VIIIa and Va to inactivate them. This anticoagulation activity can be enhanced by a presence of a cofactor such as protein S.
In hereditary thrombophilia, Coagulation Factor XIV /protein C deficiency is caused by a genetic mutation which affect protein C activity. A severe recessive form may result in massive thrombosis fatal to the patient.