Immobilization of periodate-oxidized horseradish peroxidase by adsorption on sepiolite

Horseradish peroxidases (HRP), native and periodate-oxidized were immobilized onto sepiolite clay mineral by adsorption. Both peroxidases were adsorbed on this carrier in different quantities. Specific activity of immobilized enzymes was increased with increasing the amount of peroxidase added per gram of sepiolite. The highest specific activity was achieved when 15 mg of peroxidase was added per g of sepiolite. Also, periodate-oxidized enzymes showed similar specific activity as native ones. Stability studies (pH, thermal and operational stability) were conducted for both peroxidases. Residual specific activity of HRP immobilized onto sepiolite declined with an increase of incubation time at 65 degrees C. Oxidized-peroxidase lost 64 % of the initial activity, whereas native HRP dropped 92 % of its activity after 5 min of incubation at 65 degrees C. Reduction of the enzyme activity was observed with the temperature increase from 30 to 80 degrees C. pH profiles of native peroxidase immobilized onto sepiolite were higher in both acidic and basic regions compared to periodate-oxidized enzyme. Oxidized HRP was more successful in studies of operational stability, it retained 42 % of its activity after 4 consecutive cycles of pyrogallol oxidation, whereas native peroxidase kept only 11 % of the original activity.