Coordination Chemical Studies on Metalloenzymes. IV. Kinetic and Thermodynamic Studies of Metal Removal Reaction from Zinc-and Cobalt-Carbonic Anhydrase with Chelating Agents

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The mechanism and rate of cobalt removal reaction from cobalt-enzyme with various chelating agents were investigated, in comparing with that of zinc-enzyme. The mechanism of cobalt removal reaction was the same as that of zinc-enzyme and the selectivity of chelating agents against zinc-enzyme and cobalt-enzyme was almost the same. The second-order rate constant of cobalt removal from cobalt-enzyme with various chelating agents (k_<app>) was much larger (13-30 times) than that of zinc-enzyme. The thermodynamic parameter of metal removal reaction was measured by the reaction of 5-methyl-1,10-phenanthroline with cobalt- and zinc-enzyme. Activation enthalpy for breakdown of the ternary complex of cobalt- and zinc-enzyme was almost the same (28-29 kcal mol^<-1>) but activation entropy (33 cal deg^<-1> mol^<-1>) for breakdown of the ternary complex of cobalt-enzyme was much larger than that (22 cal deg^<-1> mol^<-1>) of zinc-enzyme. This is the reason why k_<app> of the cobalt-enzyme is much larger than that of zinc enzyme.
公益社団法人日本薬学会の論文
1978-06-25