prothrombine

Prothrombin, also known as coagulation factor II, is a crucial protein in the blood clotting cascade. It is synthesized in the liver and circulates in the plasma in an inactive form. Its primary function is to be converted into thrombin, the enzyme that drives the formation of a stable fibrin clot. This conversion is a critical step in hemostasis, the process that stops bleeding.

The activation of prothrombin occurs through a series of enzymatic reactions. In the intrinsic and extrinsic pathways of coagulation, specific factors are activated, leading to the formation of the prothrombinase complex. This complex, which includes activated factor X and factor V, precisely cleaves prothrombin at specific sites. This cleavage results in the formation of thrombin.

Once activated, thrombin plays a central role in coagulation. It converts soluble fibrinogen into insoluble fibrin strands, which then polymerize to form a meshwork. This fibrin mesh traps blood cells and platelets, forming a stable clot that seals damaged blood vessels and prevents further blood loss. Thrombin also activates other clotting factors, amplifying the clotting process. The regulation of prothrombin and thrombin activity is essential to prevent excessive clotting (thrombosis) or insufficient clotting (hemorrhage).