l-Rhamnulose 1-phosphate aldolase from Escherichia coli. III. The role of divalent cations in enzyme activity
✍ Scribed by Nancy B. Schwartz; David Sidney Feingold
- Publisher
- Elsevier Science
- Year
- 1972
- Weight
- 758 KB
- Volume
- 2
- Category
- Article
- ISSN
- 0006-3061
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✦ Synopsis
~Rhanmulose l-phosphate aldolase is a zinc metallocnzyme which contains 2 g-atoms of zinc per mole of enzyme [I&f_ 2]_ A study hss been made of the effect of the metal chelator 1,lO phenanthroline on the reversible cleavage of trhamnulose 1-P catalyzed by the aldolase. 1,lO phenanthroline is an inhibitor strictly competitive with L4amnulose l-phosphate or dihydroxyacetone phosphate (DHAP), indicating involvement of zinc at the binding site of these compounds. It is a noncompetitive inhibitor with r.Jact.aldehyde, suggesting that Mactaldehyde binds to a site on the enzyme not identica1 to that for ketcse phosphate. DHAP, but not lrlactaldehyde prevents loss of zinc from the enzyme during dialysis against chelators at pH 5.0. Native r.-rhamnulosc l-phosphate aldolase and succinylated aldolasc were shown by equilibrium dialysis to bind 2 moles of DE%P per mole enzyme. &fetal-free subunits of the enzyme. or enzyme inactivated by treatment with S-hych-oxyquinoline fkulfonic acid or p-mercuribenzoic acid binds less than 1 mole of DHAP per mole of enzyme. The data suggest that each molecule of enzyme has two binding sites for DHAP and that the metal and sulfhydryl integrity of the enzyme must be maintained for binding and catalysis to occur_ Key v.-or& and phrases: zinc metalloenzyme, metal chelators, dihydroxyacetone phosphate, binding sites, equilibrium dialysis, and r.Jactaldehyde.