When these two subunits interact in the plasma, the enzyme is activated and can act within the clotting cascade. rFXIII acts by inhibiting fibrinolysis factors which enzymatically cleave the fibrin matrix, leading to the ultimate formation of clots.
The interaction of these two subunits within the plasma activates the enzyme, which then participates in the clotting process. rFXIII prevents fibrinolysis by breaking down the fibrin matrix, ultimately resulting in clot formation.