Nuclear‐Magnetic‐Resonance Studies of Carboxypeptidase B: Binding of Inhibitors to the Manganese Enzyme

Longitudinal and transverse proton relaxation rates of water in solutions of porcine manganese carboxypeptidase B have been measured in the presence of various competitive inhibitors by pulse nuclear magnetic reasonance (NMR) spectrometry. The inhibition constant of Mn‐carboxypeptidase activity by l‐argininic acid and acetyl‐l‐arginine was in agreement with the equilibrium constant obtained by the NMR method, indicating similar and specific binding of the inhibitors to the active site of the manganese enzyme. Titration of the water bound to the metal ion revealed the presence of one water molecule which could be displaced from the sphere of the manganese ion by various inhibitors. The structural features of the inhibitors required for this displacement as well as the mode of interaction is described.