The key enzyme in hemostasis that originates from a zymogen precursor, Prothrombin. Thrombin possesses distinct binding sites for substrates, inhibitors, cofactors, and sodium ions. In addition to the coagulation reaction (Thrombin conversion of Fibrinogen to fibrin), Thrombin is involved in several other proteolytic processes that maintain hemostasis: 1) activation of FXIII to further strengthen fibrin, 2) activation of FXI providing a positive feedback mechanism for additional Thrombin generation, 3) activation of cofactors FVIII and FV, 4) activation of Protein C to form Activated Protein C, a powerful anticoagulant, 5) cleavage of TAFI to form TAFIa which inhibits Plasmin (inhibits fibrinolysis), 6) cleavage of platelet PAR-1 receptor allowing for activation of platelets. The slide Coagulation Pathways (All Components) shows how Thrombin relates to the other coagulation factors. For other slide shows highlighting the critical role of Thrombin, see: Activation of Protein C by Thrombin, Activation of TAFI by Thrombin, Fibrinolytic Pathway, and Activation of Platelets by Thrombin.
