Angiotensin I-converting enzyme of the kidney cortex

Abstract

We purified the angiotensin I-converting enzyme (peptidyldipeptide hydrolase; kininase II, EC 3.4.15.1) from homogenized hog kidney cortex. For the sake of comparison, we also purified the enzyme from homogenized human lung, human kidney and hog plasma. The microsomal fraction of the homogenized swine kidney cortex contained eight times more enzyme than the corresponding fraction from homogenized swine lung. The hog kidney enzyme had a molecular weight of 195 000. It contained about 8% neutral sugars. No subunits of the converting enzyme were observed. The enzyme liberated angiotensin II from angiotensin I and inactivated bradykinin. It also hydrolyzed the fluorescent substrate I-dimethylaminonaphtalene-5-sulfonyl-glycylglycylglycine and three other substrates that were measured in the ultraviolet spectrophotometer. The ratios of rates of cleavage of dipeptides from the C-terminal end of three optically active substrates were similar for the hog plasma, kidney, and lung enzymes, but different from the human enzymes. Antibody to hog converting enzymes cross-reacted with hog lung and plasma enzymes, but not with converting enzyme of human kidney. All the enzymes tested were completely inhibited by 10 −4 M of the peptide inhibitor SQ 20881. The absence of Cl − from the buffer induced conformational changes in the structure of purified enzyme in the ultraviolet spectrophotometer.