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

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 degrees 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 degrees 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. Copyright 2010 Elsevier B.V. All rights reserved.