Thrombin

The concept of thrombin dates back to the late 19th century. In 1872, Alexander Schmidt hypothesized the existence of an enzyme that converts fibrinogen into fibrin . This hypothesis was confirmed when prothrombin, the precursor to thrombin, was discovered by Pekelharing in 1894 .

Thrombin is produced through the enzymatic cleavage of prothrombin by activated Factor X (Xa) in the presence of Factor V (Va), calcium ions, and phospholipids, forming the prothrombinase complex . This complex significantly enhances the conversion of prothrombin to thrombin. Thrombin then catalyzes the conversion of fibrinogen to fibrin, leading to the formation of a stable blood clot .

In addition to its role in clot formation, thrombin also activates several other coagulation factors, including Factor XI to XIa, Factor VIII to VIIIa, and Factor V to Va . It also plays a role in platelet activation and aggregation, further contributing to hemostasis .

Thrombin’s primary function is to convert fibrinogen into fibrin by cleaving fibrinopeptides A and B from the respective Aα and Bβ chains of fibrinogen . This process results in the formation of fibrin monomers, which polymerize to form a fibrin clot. Thrombin also activates Factor XIII, which cross-links fibrin, stabilizing the clot .

Thrombin is not only essential for normal hemostasis but also plays a role in various pathological conditions. Excessive thrombin generation can lead to thrombosis, while insufficient thrombin activity can result in bleeding disorders . Thrombin inhibitors, such as dabigatran, are used clinically to prevent and treat thromboembolic diseases .