Antithrombin III

Antithrombin III (ATIII, Serpin C1) is the principal plasma anticoagulant serpin, synthesized in the liver and circulating as a glycoprotein. It inactivates thrombin, factor Xa and factor IXa by forming stable covalent complexes, and heparin or heparan sulfate binding to its N-terminal domain accelerates thrombin inhibition by several orders of magnitude through a conformational change. Inherited antithrombin deficiency causes autosomal dominant thrombophilia with recurrent venous thromboembolism, and acquired reductions occur in sepsis, liver disease and disseminated intravascular coagulation. Glycosylation heterogeneity influences heparin affinity and plasma half-life. Both plasma-derived and recombinant antithrombin are used clinically as anticoagulants and as standards in coagulation assays.