protrombinu

Protrombina, also known as prothrombin, is a vitamin K–dependent plasma glycoprotein produced by the liver. It circulates as a zymogen (inactive enzyme) that is activated to thrombin, the central enzyme of the coagulation cascade. In the coagulation process, prothrombin is converted into thrombin by the prothrombinase complex, which includes factor Xa, factor Va, calcium ions, and a phospholipid surface. Thrombin then cleaves fibrinogen to fibrin, promotes platelet activation, and amplifies clot formation by activating factors V, VIII, XI, and XIII.

Structure and genetics: The F2 gene encodes prothrombin. The protein is synthesized as a single chain and is later proteolytically processed to generate active thrombin. Vitamin K–dependent gamma-carboxylation of several glutamate residues enables calcium binding and proper membrane association, which are essential for prothrombin's participation in coagulation.

Clinical aspects: Prothrombin levels influence clotting ability. Vitamin K deficiency, liver disease, or anticoagulants such as warfarin reduce prothrombin synthesis and prolong the prothrombin time (PT), a laboratory test used to assess the extrinsic and common pathways of coagulation. Genetic variants, such as the G20210A mutation in F2, can increase prothrombin levels and thrombosis risk, whereas severe deficiency can contribute to bleeding disorders.

Medical uses: Prothrombin complex concentrates, containing factors II, VII, IX, and X, are used for rapid reversal of anticoagulation or treatment of bleeding. Vitamin K administration helps restore gamma-carboxylation and normal coagulation in deficiency states.

See also: Coagulation cascade; Thrombin; Vitamin K.