INHIBITION BY CHELATING AGENTS OF BOVINE ERYTHROCYTE CARBONIC ANHYDRASE B AT PH 7.4

1. 1.The purified isoenzyme of carbonic anhydrase (carbonate hydro-lyase, EC 4.2.1.1) was isolated from a commercial extract by chromatography on Sephadex G-75 and DEAE-cellulose 2. 2.The kinetics of inhibition are characterized by an immediate decrease of activity following the addition of chelators. Thereafter inactivation proceeds at a slow rate. No correlation was found between the degree of inactivation and the conditional stability constants valid for the 1:1 Zn chelates. 3. 3.Using 65Zn as a tracer it could be shown that the slow inhibition is due to a mobilization of Zn from the enzyme. 4. 4.All these findings may be explained by the assumption that the immediate inactivation is caused by the formation of a ternary complex; since the Zn-protein complex is inert, the dissociation of this intermediate ternary complex, i.e. the mobilization of Zn from the enzyme, proceeds rather slowly. © 1968.