Purification of human lung angiotensin-converting enzyme

Abstract

Angiotensin-converting enzyme (ACE) was purified about 7000 times from human lung tissue obtained at thoracotomy. After solubilization with Triton X-100 and sonication, ion exchange DEAE cellulose chromatography and Sepharose 4B gel filtration were performed. After gel filtration a 5–6 fold increase in purity was achieved by neuraminidase treatment of the protein and recycling over DEAE cellulose. Purity was established in SDS electrophoresis and on electro-focusing ¹²⁵I-labelled purified protein and these procedures indicated a molecular weight of about 150,000 and PI value of 4.5, respectively. The purified protein split Angiotensin I and this action was inhibited by Captopril® (Squibb 14,225), a specific inhibitor of ACE (kininase II). The Km value for the synthetic substrate hippuryl-histidyl-leucine was 3.7 × 10^--⁴ mol/l. The IC₅₀ of Captoprila® when inhibiting human lung ACE action on the same substrate, was 4.5 × 10^--⁹ mol/l.