Isolation and characterization of angiotensin converting enzyme from human kidney

Angiotensin converting enzyme [EC 3.4.15.1] was solubilized from the membrane fraction of human kidney cortex using trypsin and purified to homogeneity by DEAE-cellulose, hydroxylapatite and DEAE-Sephadex A-50 column chromatographies, preparative isoelectric focusing, and Sephadex G-200 gel filtration. The final recovery of the enzyme was 13.9%. The molecular weight of the enzyme was estimated to be 199,000 by a sedimentation equilibrium method. A value of 170,000 was obtained for the reduced and denatured enzyme by dodecylsulfate-polyacrylamide gel electrophoresis. The enzyme was a glycoprotein consisting of a single polypeptide chain with an isoelectric point of 5.10. Neutral sugar accounted for 13% per weight of the enzyme. The purified enzyme had a specific activity of 96.9 mumol/min/mg protein for hippurylhistidylleucine. The Km value, Kcat value and hydrolytic coefficient (Kcat/Km) of the enzyme for hippurylhistidylleucine were 2.0 mM, 545 s-1 and 273 mM-1 . s-1, respectively. Rabbit antibody against the human kidney converting enzyme inhibited the activities of the enzymes from human lung and serum as equally as that from human kidney, but not those from sheep, dog, or rat sera. The human kidney and lung converting enzymes were immunologically identical on double immunodiffusion analysis.