Abstract: The activity of αamylase from porcine pancreas was enhanced under the treatment by Ce³⁺, Cd²⁺ and Pb²⁺ at a low concentration (0.5-5 μmol/L) , but was inhibited by Ce³⁺, Cd²⁺ and Pb²⁺ at a high concentration(4 or 5 μmol/Labove). Ce³⁺, Cd²⁺ and Pb²⁺ at a high concentration could competitively displace Ca²⁺ from αamylase. The equilibrium dialysis demonstrated that αamylase have five Ca²⁺binding sites with different affinities. The fluorescence titration showed that Ce³⁺, Cd²⁺ and Pb²⁺ are not only bound to Ca²⁺binding sites, but also bound to other sites of αamylase, and resulted in the αamylase conformational changes.

Key words: Amylase, Heavy metal ions, Enzyme activity, Binding site