Enzyme immobilization: Part 2: Immobilization of alkaline phosphatase on Na-bentonite and modified bentonite

Alkaline phosphatase from calf intestinal mucous membrane was immobilized on unmodified and modified bentonites. The activity of the immobilized enzyme was examined under varying experimental conditions. The effects of various factors such as concentration of enzyme solution, pH and temperature, stirring and various thermodynamic parameters were evaluated. The highest enzyme activity, for free and immobilized enzyme, was obtained in 0.1 M phosphate buffer at pH 7. Optimal enzyme activity of both free and adsorbed enzyme was reached at pH = 10. The best time period of magnetic stirring was 2 h at 4 °C. The adsorption isotherm was modeled by Langmuir equation. The effect of substrate concentration on enzymatic activity of the free and immobilized enzymes showed a good fit to the Michaelis–Menten plots. The immobilized enzyme exhibited activity comparable to the soluble enzyme after storage at 30 °C. Thermal stability and resistance against proteolytic attack were also evaluated.