Which enzyme acts on fibrin during the process of fibrinolysis?

Plasmin is the enzyme responsible for the breakdown of fibrin in the process of fibrinolysis. Fibrinolysis is the physiological process that prevents blood clots from growing and becoming problematic by dissolving fibrin, the primary component of blood clots.

Plasmin is formed from its inactive precursor, plasminogen, which is incorporated into the clot. When activated by tissue plasminogen activator (tPA) or urokinase, plasmin cleaves fibrin strands, leading to the dissolution of the clot. This is a vital mechanism for maintaining proper blood flow and ensuring that excessive clot formation does not occur in response to injury.

The other enzymes mentioned do not play a direct role in the fibrinolysis process. Thrombin primarily facilitates clot formation by converting fibrinogen to fibrin, while Factor Xa is a critical component in the coagulation cascade that leads to thrombin generation. Protein C is involved in the regulation of coagulation but not specifically in the degradation of fibrin. Thus, plasmin is uniquely responsible for the enzymatic action on fibrin during fibrinolysis.