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 presence of captopril, lisinopril and enalapril were investigated in kidney, lung and serum of sheep using Hip-His-Leu(HHL) as substrate. The activity in kidney, lung and serum was inhibited at HHL concentration above 5 mM. The inhibitory constants (IC₅₀) ranged between 5.6 nM for serum ACE with lisinopril and 70000 nM for renal ACE with enalapril while K₁ ranged from 1.0 nM for serum ACE with lisinopril to 12000 nM for kidney ACE with enalapril. Differences in inhibition observed in different tissues suggest that the inhibitors may block function(s) of ACE to varying degrees in each tissue.