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Biochemistry of Prothrombin
Molecular mass
- 37 000 D α-Thrombin
- 72 000 D Prothrombin
Plasma concentration: 100 – 150μg/ml
Half-life: 72 hours
Normal range: 70 – 130%
Thrombin (Factor IIa) is the central enzyme of the coagulation system. The arginin-specific serine protease circulates in plasma as inactive zymogen (prothrombin, factor II) and is activated by the prothrombinase complex (factor Xa, factor Va, phospholipids and calcium ions). The procoagulant effect of thrombin is cleavage of fibrinogen into soluble fibrin monomers, which will then polymerise to form the insoluble fibrin clot. This polymerization process is catalyzed by factor XIII, which is also activated by thrombin. Thrombin also displays an important anticoagulant activity; in complex with thrombomodulin it activates protein C, which inhibits coagulation by degradation of the activated coagulation factors Va and VIIIa.
Clinical significance of Prothrombin
In rare cases of hereditary thrombophilia mutations in the thrombin molecule can be detected, which show normal procoagulant activity, but only slight anticoagulant activity. A recently discovered mutation G → A in the 3′-untranslated region of the prothrombin gene at position 20210 leads to increased prothrombin concentrations in plasma in the majority of the affected subjects which in turn leads to an increased risk of venous and arterial thrombosis.
Clinical or Research use of Prothrombin
- Suspected inherited thrombophilia
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