Immobilization of acid phosphatase on uncalcined and calcined Mg/Al-CO 3 layered double hydroxides

Abstract

Acid phosphatase was immobilized on layered double hydroxides of uncalcined- and calcined-Mg/Al-CO 3 (Unc-LDH-CO 3, C-LDH-CO 3) by the means of direct adsorption. Optimal pH and temperature for the activity of free and immobilized enzyme were exhibited at pH 5.5 and 37 °C. The Michaelis constant ( K m ) for free enzyme was 1.09 mmol mL −1 while that for immobilized enzyme on Unc-LDH-CO 3 and C-LDH-CO 3 was increased to 1.22 and 1.19 mmol mL −1, respectively, indicating the decreased affinity of substrate for immobilized enzymes. The residual activity of immobilized enzyme on Unc-LDH-CO 3 and C-LDH-CO 3 at optimal pH and temperature was 80% and 88%, respectively, suggesting that only little activity was lost during immobilization. The deactivation energy ( E d ) for free and immobilized enzyme on Unc-LDH-CO 3 and C-LDH-CO 3 was 65.44, 35.24 and 40.66 kJ mol −1, respectively, indicating the improving of thermal stability of acid phosphatase after the immobilization on LDH-CO 3 especially the uncalcined form. Both chemical assays and isothermal titration calorimetry (ITC) observations implied that hydrolytic stability of acid phosphatase was promoted significantly after the immobilization on LDH-CO 3 especially the calcined form. Reusability investigation showed that more than 60% of the initial activity was remained after six reuses of immobilized enzyme on Unc-LDH-CO 3 and C-LDH-CO 3. A half-life ( t 1/2) of 10 days was calculated for free enzyme, 55 and 79 days for the immobilized enzyme on Unc-LDH-CO 3 and C-LDH-CO 3 when stored at 4 °C. Therefore, immobilization of acid phosphatase on Unc-LDH-CO 3 and C-LDH-CO 3 by direct adsorption is an effective means and would have promising potential for the practical application in agricultural production and environmental remediation.