Synthesis<unk>  is produced by<unk> e enzymatic cleavage of two sites on prothrombin by activated Factor X (Xa).<unk> e activity of factor Xa is greatly enhanced by binding to activated Factor V (Va), termed<unk> e prothrombinase complex. Prothrombin is produced in<unk> e liver and is co-translationally modified in a vitamin K-dependent reaction<unk> at converts 10-12 glutamic acids in<unk> e N terminus of<unk> e molecule to gamma-carboxyglutamic acid (Gla). In<unk> e presence of calcium,<unk> e Gla residues promote<unk> e binding of prothrombin to phospholipid bilayers. Deficiency of vitamin K or administration of<unk> e anticoagulant warfarin inhibits<unk> e production of gamma-carboxyglutamic acid residues, slowing<unk> e activation of<unk> e coagulation cascade. In human adults,<unk> e normal blood level of antithrombin activity has been measured to be around 1.1 units/mL. Newborn levels of<unk>  steadily increase after birth to reach normal adult levels, from a level of around 0.5 units/mL 1 day after birth, to a level of around 0.9 units/mL after 6 months of life. Mechanism of action In<unk> e blood coagulation pathway,<unk>  acts to convert factor XI to XIa, VIII to VIIIa, V to Va, fibrinogen to fibrin, and XIII to XIIIa. In<unk> e conversion of fibrinogen into fibrin,<unk>  catalyzes<unk> e cleavage of fibrinopeptides A and B from<unk> e respective Aα and Bβ chains of fibrinogen to form fibrin monomers. Factor XIIIa is a transglutaminase<unk> at catalyzes<unk> e formation of covalent bonds between lysine and glutamine residues in fibrin.<unk> e covalent bonds increase<unk> e stability of<unk> e fibrin clot.<unk>  interacts with<unk> ombomodulin. As part of its activity in<unk> e coagulation cascade,<unk>  also promotes platelet activation and aggregation via activation of protease-activated receptors on<unk> e cell membrane of<unk> e platelet. Negative feedback<unk>  bound to<unk> ombomodulin activates protein C, an inhibitor of<unk> e coagulation cascade.<unk> e activation of protein C is greatly enhanced following<unk> e binding of<unk>  to<unk> ombomodulin, an integral membrane protein expressed by endothelial cells. Activated protein C inactivates factors Va and VIIIa. Binding of activated protein C to protein S leads to a modest increase in its activity.<unk>  is also inactivated by antithrombin, a serine protease inhibitor.
Thrombin
Prothrombinase
Platelet-activating factor
Kallikrein
Plasminogen 
Fibrinolysin
Von Willebrand factor
Serpin