Angiotensin-converting enzyme (EC 3.4.15.1), or ACE, is a central component of the renin–angiotensin system (RAS), which controls blood pressure by regulating the volume of fluids in the body. It converts the hormone angiotensin I to the active vasoconstrictor angiotensin II. Therefore, ACE indirectly increases blood pressure by causing blood vessels to constrict. ACE inhibitors are widely used as pharmaceutical drugs for treatment of cardiovascular diseases.The enzyme was discovered by Leonard T. Skeggs Jr. in 1956. The first crystal structure of human testis ACE was solved in the year 2002 by R. Natesh in the lab of K. Ravi Acharya and the work was published in the journal Nature in January 2003. It is located mainly in the capillaries of the lungs but can also be found in endothelial and kidney epithelial cells.Other less known functions of ACE are degradation of bradykinin, substance P and amyloid beta-protein.