Inhibition of cobalt(II) carboxypeptidase A by ligands. Kinetic evidence for the formation of a ternary enzyme-metal-ligand complex

Saturation kinetics are observed in the inhibition of cobalt carboxypeptidase A by the chelating agent 1,10-phenanthroline. The association constant K₁ for the formation of the enzyme-metal-ligand ternary complex and k₂, the rate of breakup of the ternary complex, have been obtained. A mechanism is proposed to account for the pH profile of the reaction which, in conjunction with K₁, permits the calculation of the individual rate constants k₁, K_?1, k₂, k₃. The magnitude of the rate constant k₁ suggests that cobalt(II) in CoCPA is five-coordinate. Similar but less extensive studies on inhibition by 2,2′-bipyridyl and 8-hydroquinoline-5-sulfonic acid have also been carried out