Protrombinem

Protrombinem is the instrumental case in Polish medical terminology for protrombin, known in English as prothrombin. Prothrombin is a vitamin K–dependent plasma glycoprotein and one of the coagulation factor proteins designated as factor II. It is produced by hepatocytes as a single, inactive zymogen and serves as the precursor to thrombin, a key enzyme in blood coagulation.

Structure and synthesis

Prothrombin contains a gamma-carboxyglutamate (Gla)–rich N-terminal domain that requires vitamin K–dependent carboxylation, two kringle domains, and a C-terminal serine protease domain. This structure enables binding to phospholipid surfaces in a calcium-dependent manner, facilitating its participation in the coagulation cascade. The F2 gene encodes prothrombin.

Activation and function

Prothrombin is activated to thrombin by the prothrombinase complex, formed by factor Xa and factor Va on activated platelets in the presence of calcium ions and phospholipids. Thrombin then converts fibrinogen to fibrin, activates multiple coagulation factors, and promotes platelet activation, amplifying the coagulation response. Prothrombin thus acts as a pivotal link between the initial coagulation triggers and the final formation of a stable fibrin clot.

Clinical relevance

Abnormal prothrombin levels or function can lead to bleeding disorders or thrombotic tendencies. Hereditary prothrombin deficiencies are rare; a common variant, the prothrombin G20210A mutation, is associated with increased thrombotic risk. Warfarin therapy reduces gamma-carboxylation of prothrombin, lowering functional prothrombin levels. Prothrombin time (PT) tests, often reported as INR, assess the extrinsic pathway and are used to monitor anticoagulant therapy and liver function.