Fig. 25.12 Crystal structure of lisinopril 25.19 (Fig.25.11) with t-ACE. The central carboxylate group of the inhibitor coordinates to the zinc ion. The NH group on the lysine residue of lisinopril forms an H-bond to the C═O group of Ala354 in the S1′ pocket, and the carbonyl group also forms hydrogen bonds with His353 and His513. The terminal ammonium group of the lysine residue forms an H bond to Glu162. The acid group of the proline residue forms an H-bond contact with Lys511 and Tyr520. The phenethyl side chain is placed in the S1 pocket.