Proteolytic modulation of factor Xa-antithrombin complex enhances fibrinolysis in plasma

► The fibrinolytic fragment of clotting factor Xa (Xa), Xa33/13, was found in plasma. ► A source of Xa33/13 in plasma is from the Xa-antithrombin (XaAT) complex. ► Conversion of Xa to Xa33/13 occurs at least 10-fold faster in complex with AT. ► XaAT accelerates plasma clot lysis and plasmin generation by tPA better than FXa. ► A novel function for XaAT was identified that links coagulation to fibrinolysis.