A serine protease inhibitor (serpin) and natural anticoagulant:
- Physiologically inactivates
- Thrombin (factor IIa)
- Factor Xa (FXa)
- To a lesser extent:
- Factor IXa
- FXIa
- FXIIa
- Tissue plasminogen activator (t-PA)
- Urokinase
- Trypsin
- Plasmin
- Kallikrein
- Alpha2-globulin synthesized predominantly in the liver
- Molecular weight of 58,200 Da
- Half-life of approximately 2.4 days
- Anticoagulant effect of AT is accelerated at least a thousand times in the presence of heparin (heparin is a co-factor):
- Requires the binding of a unique sequence-specific pentasaccharide domain of heparin to the heparin-binding domain of AT.
- This interaction induces a conformational change in AT, which accelerates the inhibition of FXa.
- The inhibition of thrombin, in addition, requires heparin to bind to both AT and thrombin, to form a ternary bridging complex, so that then thrombin can be inhibited.
- In addition to its anticoagulant role, AT has been found to have an important anti-inflammatory effect that occurs in relation to its interaction with the endothelium.
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