In this reaction, all reactants and products are invisible. The heat being evolved is the clue that tells you a reaction is taking place. This is a good example of an exothermic reaction, a reaction in which heat is given off. A lot of reactions are exothermic.
Prothrombinase will cleave prothrombin to make thrombin and thrombin is the enzyme that cuts fibrinogen to make fibrin for clot formation [Blood Clotting: The Basics]. The platelet prothrombinase activity is the same as the activity on TP-bearing cells: itâs formed from Xa and membrane-bound Va.
Clinical Background. Prothrombin, or factor II, is the precursor of thrombin; as such, it plays a key role in the balance between procoagulation and anticoagulation. A prothrombin genetic variant known as 20210G A is associated with elevated levels of prothrombin and with thrombophilia.