• A plasma protein that is the inactive precursor of thrombin. It is converted to thrombin by a prothrombin activator complex consisting of factor Xa, factor V, phospholipid, and calcium ions. Deficiency of prothrombin leads to hypoprothrombinemia.
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2021
• Plasma protein precursor of thrombin, converted to thrombin by a prothrombin activator complex; deficiency of prothrombin leads to hypoprothrombinemia.
  CRISP Thesaurus
  National Institutes of Health, 2006
• Clotting factor II, or prothrombin, is a vitamin K�dependent proenzyme that functions in the blood coagulation cascade. Factor II deficiency is a rare, inherited or acquired bleeding disorder.
  Medscape
  WebMD, 2019
• Prothrombin, glycoprotein (carbohydrate-protein compound) occurring in blood plasma and an essential component of the blood-clotting mechanism. Prothrombin is transformed into thrombin by a clotting factor known as factor X or prothrombinase; thrombin then acts to transform fibrinogen, also present...
  Encyclopedia Britannica
  Encyclopedia Britannica, Inc., 2020