The thrombin-fibrinogen interaction.

The thrombin-catalyzed conversion of fibrinogen (F) to fibrin consists of three reversible steps, with thrombin (T) being involved in only the first step which is a limited proteolysis to release fibrinopeptides (FpA and FpB) from fibrinogen to produce fibrin monomer. In the second step, fibrin monomers form intermediate polymers through noncovalent interactions. In the third step, the intermediate polymers aggregate to form the fibrin clot. The molecular mechanisms of the first two steps are elucidated.