Isolation of human liver angiotensin-converting enzyme by chromatofocusing

Angiotensin-converting enzyme (EC 3.4.15.1) has been isolated from human liver by chromatofocusing. The isolation procedure permitted us to obtain a 9000-fold purified enzyme with a 22% yield. Specific activity of the angiotensin-converting enzyme was 10 units/mg of protein. The molecular mass of enzyme determined by polyacrylamide gel electrophoresis under denaturing conditions was 150,000. The isoelectric point (4.2-4.3) was also determined by chromatofocusing. The Km values of the enzyme for hippuryl-L-histidyl-L-leucine and N-benzyloxycarbonyl-L-phenylalanyl-L-histidyl-L-leucine are 5000 and 125 microM, respectively. The human liver angiotensin-converting enzyme is inhibited by bradykinin-potentiating factor SQ 20881 (IC50 = 18 nM).