The function of the metal ion in leucine aminopeptidase and the mechanism of action of the enzyme

Abstract

Leucine aminopeptidase is reversibly inactivated by incubation with EDTA. In the presence of p-chloro-mercuribenzoate this inactivation is irreversible. Substrate, leucine and cysteine prevent the reconstitution of the metal ion-free enzyme with Mg2+ ions. Evidence has been obtained that the esterase and peptidase activities occur at the same catalytic site. The activation of the enzyme by Mn2+ ions is a slow process, the rate-limiting step of which is the dissociation of the Mg2+ ion-enzyme complex. Evidence is presented that the metal ion-binding sites are the same for leucine aminopeptidase, glycylglycine dipeptidase, glycyl-leucine dipeptidase, prolidase, carnosinase and carboxypeptidase. A mechanism is presented for the action of leucine aminopeptidase.