Abstract: Inhibiting effects of heavy metal ions on urease-catalyzed reaction were investigated with micro-calorimetry. Further, the joint inhibition effects of two heavy metal ions on urease-catalyzed reaction were also conducted. The results indicate that, with a wide range of concentration(0.1, 1, 10, 100 and 10³ mg/L), heavy metal ions not only inhibit urease hydrolysis reaction, but also can promote this reaction in some concentration range. For instance, inhibition rate is (0.49?0.20)% and (-11.93?1.34)% when Cu²⁺concentration is 100 and 1000 mg/L, respectively. The correlation between urease inhibition rate and concentration of heavy metal ion is very significant, and the inhibition effects are: As³⁺>Pb²⁺>Cd²⁺>Cu²⁺. The joint inhibition is close to that with higher inhibition when two heavy metal ions are used together. This work proves that the micro-calorimetry may be a potential method to rapidly and accurately detect heavy metals.

Key words: Micro-calorimetry, Enzyme inhibition, Heavy metal ion, Inhibition rate, Joint inhibition