Tissue plasminogen activator (t-PA) is a protein involved in breaking down the blood clot. It is a serine protease found in the endothelial cells that line blood vessels. Like any enzyme, it converts plasminogen into plasmin, the main blood clot lysis enzyme. Due to its lysis activity, t-PA is used in clinical medicine to treat cerebral embolism and thrombosis. Its use is contraindicated in cases of cerebral hemorrhage or head trauma.