Prothrombins

Prothrombins are a group of vitamin K-dependent proteins, with prothrombin (also known as Factor II) being the most prominent example. Prothrombin is a crucial zymogen, an inactive precursor to the enzyme thrombin, which plays a central role in blood coagulation. The synthesis of prothrombin occurs in the liver, and its activation is a complex cascade involving other clotting factors. Vitamin K is essential for the post-translational modification of prothrombin, allowing it to bind calcium ions and phospholipids, which are vital for its proper function within the coagulation pathway. Upon activation, prothrombin is cleaved to form thrombin. Thrombin then acts as a serine protease, converting soluble fibrinogen into insoluble fibrin, which forms the meshwork of a blood clot. The intricate regulation of prothrombin levels and its activation is critical for preventing both excessive bleeding and the formation of inappropriate blood clots, such as those that can lead to thrombosis. Genetic deficiencies in prothrombin can result in bleeding disorders.