Hemostasis Coagulation Practice Test

Fibrinolysis dissolves clots through plasmin, a serine protease that cleaves fibrin to break down the clot. The body’s main trigger for generating plasmin is tissue plasminogen activator, a serine protease released by endothelial cells that converts plasminogen to plasmin directly at the clot site. This makes tissue plasminogen activator the key enzyme initiating clot breakdown.

Alpha-2 antiplasmin inhibits plasmin, so it protects clots rather than driving breakdown. PAI-1 inhibits the activators (including tPA and uPA), reducing fibrinolysis rather than acting as the protease. Streptokinase activates plasminogen indirectly but is not a human serine protease; it forms a complex to promote plasmin formation, whereas the principal serine protease driving the process is tPA.

So, the best answer is tissue plasminogen activator.