Final answer:
The enzyme angiotensin-converting enzyme (ACE) catalyzes the conversion of angiotensin I to angiotensin II in the renin-angiotensin-aldosterone pathway. This process is essential for the regulation of blood pressure and fluid balance in the body.
Step-by-step explanation:
The step of the renin-angiotensin-aldosterone pathway that is catalyzed by angiotensin-converting enzyme (ACE) is the conversion of angiotensin I to angiotensin II. This critical reaction occurs primarily in the lungs. ACE has a crucial role in the regulation of blood pressure and fluid balance within the body. When blood volume or pressure is low, renin is secreted by the kidneys and acts on angiotensinogen, which is produced by the liver, converting it into angiotensin I. This inactive form circulates in the bloodstream to the lungs, where ACE catalyzes the transformation of angiotensin I into the active angiotensin II. Angiotensin II then functions to constrict blood vessels, increase blood pressure, and promote the release of aldosterone and anti-diuretic hormone (ADH), which help to raise blood volume and pressure to homeostatic levels.