Angiotensin I [Phe8-His9] hydrolase and bradykininase from human lung.

Atypical angiotensin I “converting enzyme” (angiotensin I [Phe⁸-His⁹] hydrolase or APHH) was purified from human lung tissue. Two enzyme preparations from different lungs were found to fragment and inactive bradykinin. Fragmentation was demonstrated by electrophoretic techniques and biological inactivation was demonstrated by bioassay. Bradykininase activity was inhibited by low concentrations of 2,3-dimercaptol-propanol (BAL) and ethylenediaminetetraacetic acid (EDTA), but not by phenylmethylsulfonyl fluoride (PMSF) or p-chloromercuriphenyl sulfonic acid (CMPSA). Conversion of angiotensin I was inhibited by BAL, PMSF, and CMPSA but not by EDTA. APHH from a third lung preparation was free of significant bradykininase activity as determined by bioassay. It is concluded that these two enzymatic activities are probably associated with separate enzymes.