Abstract
A simple method was set up to isolate, partially purify and characterize angiotensin-converting enzyme from rabbit lungs. Angiotensin-converting enzyme was purified by a three-step method: Ammonium sulphate precipitation (30-70%), gel filtration chromatography (Sephadex G-75) and ion exchange chromatography (CM-sephadex). The enzyme activity was assayed by monitoring the rate of production of hippuric acid from the hydrolysis of Hippuryl-L-Histidine-L-Leucine by angiotensin-converting enzyme. From the results, the enzyme was purified 6.25-fold with a yield of 21% on CM-Sephadex column. The angiotensin converting enzyme from rabbit lung had a broad optimum pH range (8.0-8.3) and optimum temperature of 37°C. Initial velocity studies for the determination of kinetic constants with Hippuryl-L-Histidine-L-Leucine as substrate revealed a KM and VMAX of 1.8 and 0.4 μmol min-1, respectively. The enzyme activity was not affected by Mg2+, Ca2+, Na+ and K+, while EDTA strongly inhibited it. In conclusion, this study has shown that though angiotensin-converting enzyme can be partially-purified from rabbit lungs via. a three-step purification protocol, the purification steps and assay conditions needs to be modified to obtain a higher yield and specific activity