Most important serine protease inhibitor in plasma that regulates the blood coagulation cascade (PubMed:15853774, PubMed:15140129). AT-III inhibits thrombin, matriptase-3/TMPRSS7, as well as factors IXa, Xa and XIa (PubMed:15140129). Its inhibitory activity is greatly enhanced in the presence of heparin. Forms protease inhibiting heterodimer with TMPRSS7. Found in plasma. Phosphorylated by FAM20C in the extracellular medium. Variant Thr-414. The disease is caused by variants affecting the gene represented in this entry. Belongs to the serpin family. Antithrombin entry