Metal binding stoichiometry and mechanism of metal ion modulation of the activity of porcine kidney leucine aminopeptidase

Abstract

Porcine kidney leucine aminopeptidase has been obtained from commercial sources as in inhomogeneous preparation with variable metal content and purified by affinity chromatography over L-leucylglycyl-AH-Sepharose. Treatment with Zn2+ followed by gel filtration restores the Zn2+ content of the native enzyme, which is 6 mol of Zn2+ per hexamer, each of which is located in a single catalytic binding site per subunit. The activity of the native enzyme is modulated by incubation with divalent metal ions; it is activated by Mn2+ and Mg2+ and inhibited by Ni2+, Cu2+, Zn2+, Hg2+ and Cd2+. These metals modulate the activity by binding to a separate site on each subunit, referred to as the regulatory site. Binding of these metals at the regulatory site alters the activity of the enzyme by changing kcat, leaving KM unaltered. The number and nature of the metal binding sites of porcine kidney leucine aminopeptidase are very similar to those of the enzyme from bovine lens.