Mechanism of heavy metal ions on alpha-amylase activity from porcine pancreas

The activity of a-amylase from porcine pancreas was enhanced under the treatment by Ce3+, Cd2+ and Pb3+ at a low concentration (0.5-5 mu mol/L), but was inhibited by Ce3+, Cd2+ and Pb2+ at a high concentration (4 or 5 mu mol/L above). Ce3+, Cd2+ and Pb2+ at a high concentration could competitively displace Ca2+ from alpha -amylase. The equilibrium dialysis demonstrated that alpha -amylase 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 alpha -amylase, and resulted in the alpha -amylase conformational changes.