INHIBITION OF ANGIOTENSIN-CONVERTING ENZYME FROM SHEEP TISSUES BY CAPTOPRIL, LISINOPRIL AND ENALAPRIL

Inhibition of angiotensin converting enzyme(EC 3.4.15.1, ACE) in prese nce of captopril, lisinopril and enalapril were investigated in kidney , lung and serum of sheep using Hip-His-Leu(HHL) as substrate. The act ivity in kidney, lung and serum was inhibited at HHL concentration abo ve 5 mM. The inhibitory constants (IC50) ranged between 5.6 nM for ser um BCE with lisinopril and 70000 nM for renal ACE with enalapril while K-i ranged from 1.0 nM for serum ACE with lisinopril to 12000 nM for kidney BCE with enalapril. Differences in inhibition observed in diffe rent tissues suggest that the inhibitors may block function(s) of a AC E to varying degrees in each tissue.