title: Characteristics of angiotensin converting enzyme and its role in the metabolism of angiotensin I by endothelium.
abstract: Angiotensin converting enzyme (ACE) was isolated from rabbit lung tissue by affinity chromatography on an N-(1-carboxy-5-aminopentyl)-L-alanylglycine resin. The molecular weight of the enzyme was determined to be 140,000, and upon isoelectric focusing a set of bands between pH 4.3-4.7 was observed. When the enzyme was treated with endoglycosidase F the molecular weight decreased to 100,000, and a virtually identical molecular weight was found for the in vitro translated form of ACE. The ACE-catalyzed hydrolysis of angiotensin I was followed by high-performance liquid chromatography separation and fluorescence monitoring of substrate and products. The kinetic parameters of the angiotensin I hydrolysis were KM = 17 mumol/L and kcat = 420 min-1 at pH 7.5. By the same analytical method the metabolism of angiotensin I by cultured endothelial cells and by the isolated, perfused rabbit aorta was investigated. Only a small fraction of angiotensin I was converted to angiotensin II; the larger part was directly degraded to small peptides. In the presence of ACE inhibitors no angiotensin II was formed but the rate of the angiotensin I hydrolysis was virtually unchanged. Thus, the action of ACE is critical to the generation of angiotensin II but not to the degradation of angiotensin I, and during ACE inhibition no accumulation of angiotensin I occurs.
mesh_terms: D000803:Angiotensin I / Q000378:metabolism*; D000806:Angiotensin-Converting Enzyme Inhibitors; D000818:Animals; D001011:Aorta / Q000378:metabolism; D004727:Endothelium / Q000378:metabolism*; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000378:metabolism; D007703:Peptidyl-Dipeptidase A / Q000378:metabolism*; D011817:Rabbits; D012084:Renin-Angiotensin System
chemical_list: D000806:Angiotensin-Converting Enzyme Inhibitors; D000803:Angiotensin I; D007703:Peptidyl-Dipeptidase A