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.
Thrombin is produced by the enzymatic cleavage of two sites on prothrombin by activated Factor X (Xa). The activity of factor Xa is greatly enhanced by binding to activated Factor V (Va), termed the prothrombinase complex. Prothrombin is produced in the liver and is co-translationally modified in a vitamin K-dependent reaction that converts ten glutamic acids on prothrombin to gamma-carboxyglutamic acid (Gla).