Spectrophotometric assay and properties of the angiotensin-converting enzyme of rabbit lung

✍ Scribed by D.W. Cushman; H.S. Cheung

• Book ID: 115770885
• Publisher: Elsevier Science
• Year: 1971
• Tongue: English
• Weight: 963 KB
• Volume: 20
• Category: Article
• ISSN: 0006-2952
• DOI: 10.1016/0006-2952(71)90292-9

✦ Synopsis

A sensitive, fixed-time, spectrophotometric assay for angiotensin-converting enzyme measures the rate of production of hippuric acid from hippuryl-L-histidyl-L-leucine (HHL). The angiotensin-converting enzyme from rabbit lung acetone powder extract, when assayed by this method, is optimally active at pH 8.1 to 8.3 at a chloride ion concentration of 300 mM and an HHL concentration of 5–10 mM; the K

m
for HHL is 2–6 mM. The enzyme was inhibited by metal-chelating agents, heavy metal salts and certain peptides. The most effective inhibitors were EDTA; CdBr2; angiotensin II; bradykinin; and a pentapeptide, L-pyroglutamyl-L-lysyl-L-tryptophyl-L-alanyl-L-proline, a component of Bothrops jararaca venom. Enzyme inhibited by 0.1 mM EDTA was completely reactivated after removal of EDTA by dialysis but, after prolonged dialysis of the enzyme against 1 mM EDTA, reactivation could only be achieved by addition of metal ions: MnCI2 (40%), ZnCl2 (100%) or Co(NO3)2 (160%). The angiotensin-converting enzyme of rabbit lung is a stable, chloride ion-activated metalloenzyme, similar to both the angiotensin-converting enzyme and kininase II of plasma.