A. Prothrombin activator, prothrombin, thrombin
Work Step by Step
Platelets and injured tissues release a prothrombin activator at the site of a damaged blood vessel. This prothrombin activator converts prothrombin into thrombin. Thrombin then acts as an enzyme that severs two amino acid chains from a fibrinogen molecule. These severed amino acid chains bond together to form a blood clot.