Angiotensin I-converting enzyme (ACE, EC 3.4.15.1), an exopeptidase, is a circulating enzyme that participates in the body's renin-angiotensin system (RAS), which mediates extracellular volume (i.e. that of the blood plasma, lymph and interstitial fluid), and arterial vasoconstriction. It is secreted by pulmonary and renal endothelial cells and catalyzes the conversion of decapeptide angiotensin I to octapeptide angiotensin II. Description: Rabbit lung. Alternative Names: CD143 protein, Angiotensin Converting Enzyme protein, Peptidyl-dipeptidase A protein, Peptidyldipeptide Hydrolase protein