Angiotensin-converting enzyme (ACE) is an important protein in the body that helps regulate blood pressure. It converts angiotensin I, an inactive precursor, into angiotensin II, a potent vasoconstrictor. This process increases blood pressure by narrowing blood vessels and stimulating the release of hormones that promote fluid retention. ACE is primarily found in the lungs and plays a crucial role in the renin-angiotensin system, which controls blood pressure and fluid balance. Medications that inhibit ACE, known as ACE inhibitors, are commonly used to treat conditions like hypertension and heart failure by preventing the formation of angiotensin II.