Electron paramagnetic resonance studies of cobalt-substituted angiotensin I-converting enzyme

Electron paramagnetic resonance (EPR) spectroscopy has been used to study the metal coordination sphere geometry in the cobalt-substituted Zn-protein angiotensin I-converting enzyme (ACE). It has been shown that ACE contains two distinct metal-binding sites. In the presence of the two structurally different inhibitors, captopril and ramiprilat, it is found that the metal binding sites are nearly structurally identical and are separated more than 10 Angstrom from each other. The metal atoms are most likely four- to five-coordinated, and it is argued that the inhibitor binds directly to the metal ion.