protrombiinasekompleksin

Protrombiinasekompleksin, also known as the prothrombinase complex, is a crucial enzymatic assembly involved in the blood coagulation cascade. It is a large protein complex that catalyzes the conversion of prothrombin (factor II) into thrombin (factor IIa). This conversion is a key step in hemostasis, the process by which bleeding is stopped.

The prothrombinase complex is assembled on the surface of activated platelets. Its primary components are factor Xa (activated factor X) and factor Va (activated factor V). Factor Xa is the enzyme that directly cleaves prothrombin, while factor Va acts as a cofactor, significantly accelerating the reaction rate. The complex is further stabilized by the presence of calcium ions and phospholipids provided by the activated platelet membrane.

The formation of thrombin by the prothrombinase complex is a highly amplified process. A small amount of factor Xa can generate a large quantity of thrombin, which then plays a central role in clot formation. Thrombin converts soluble fibrinogen into insoluble fibrin, forming a mesh that traps blood cells and platelets, thus forming a stable clot. The activity of the prothrombinase complex is tightly regulated to prevent excessive clot formation and thrombosis. Inhibitors like antithrombin and protein C contribute to this regulation. Defects in the components of the prothrombinase complex or its regulatory mechanisms can lead to bleeding disorders or thrombotic events.