Coordination chemical studies on metalloenzymes. Kinetics and mechanism of the Zn(II) exchange reaction between chelating agent and apo-bovine carbonic anhydrase.

The mechanism of removal of the zinc ion from bovine carbonic anhydrase [EC 4.2.1.1] (BCA) by a chelating agent was studied. It was shown that the removal of the zinc ion from BCA took place through the formation of a ternary complex involving the enzyme, chelating agent, and metal ions. The formation constant of the ternary complex (KEML) was 10(2) M-1. This value was lower than the formation constant assumed by Wilkins. The reaction of zinc-2, 6-pyridinedicarboxylate complex with the apoenzyme also took place through the formation of the ternary complex and the species which reacted with apo-BCA was a 1:1 complex of zinc and 2, 6-pyridine-dicarboxylate. The theoretical equilibrium equation derived from the reaction mechanism showed a good fit with observed equilibrium dialysis data.