Effect of tetranitromethane on the aldolase and [beta]-decarboxylase activities of bovine liver 2-keto-4-hydroxyglutarate aldolase

Abstract

Treatment of bovine liver 2-keto-4-hydroxyglutarate aldolase with tetranitromethane at pH 8.0 and room temperature rapidly and irreversibly destroys two known catalytic properties of this enzyme, namely, the reversible aldolytic cleavage of 2-keto-4-hydroxyglutarate and also the [beta]-decarboxylation of oxaloacetate. Loss of both enzymatic activities proceeds at the same rate and to the same extent with low molar quantities of tetranitromethane. 2-Keto-glutarate, a competitive inhibitor, protects the enzyme against inactivation by this reagent. The rate of inactivation increases with increasing pH and corresponds well with the pH dependency of aldolase activity. Identical inactivation kinetics are obtained regardless of whether the - or the -isomer of 2-keto-4-hydroxyglutarate is used as substrate. The results are consistent with the proposal that tetranitromethane modifies an active site (or sites) involved in both the aldolase and [beta]-decarboxylase activities of the enzyme.