Subcellular Localization and Partial Purification of a Chloride Dependent Angiotensin‐i Converting Enzyme From Rat Brain

Abstract— Angiotensin converting enzyme (peptidyl dipeptide hydrolase EC 3.4.15.1) was extracted from particulates of rat brain using the nonionic detergent Triton X‐100. Enzyme activity in subcellular fractions was associated with purified synaptosomes and present in the microsomal fraction, but absent in purified mitochondria and water‐shocked myelin. Partial purification was achieved by chromatography on DEAE‐cellulose and hydroxylapatite columns. The enzyme had a pH optimum of pH 7–8 and an apparent K m of 2.2 m m using hippuryl‐histidyl‐leucine as substrate; it was chloride dependent, inhibited by (Sar 1 ‐Ala 8 )‐angiotensin‐II (saralasin), and, at lower concentrations, by the specific nonapeptide inhibitor SQ 20881. Associated with the purified enzyme was an aminopeptidase, cleaving N‐terminal Asp from the native substrate, which could be involved in the production of the active heptapeptide, angiotensin III (des‐Asp‐angiotensin‐II). Also present was a carboxypeptidase‐like enzyme removing C‐terminal Phe following the liberation of His‐Leu by converting enzyme, which may be involved in the inactivation of angiotensin II or III.