Covalent immobilization of aminoacylase to alginate for L-phenylalanine production

Stability of alpha-amylase immobilized on poly(methyl methacrylate-acrylic acid) microspheres

Poly(methyl methacrylate-acrylic acid) microspheres were prepared and the acid groups were activated by using either carbodiimide (CDI) or thionyl chloride (SOCl2). alpha-Amylase was covalently bound on these activated microspheres. The properties of the immobilized enzyme were investigated and compared with those of the free enzyme. The relative activities were found to be 80.4 and 67.5% for carbodiimide and thionyl chloride bound enzymes, respectively. Maximum activities were obtained at lower pHs and higher temperatures upon immobilization compared to free enzyme. No change in Vmax and approximately 12-fold increase in K(m) were observed for immobilized enzymes. The enzyme activities, after storage for 1 month, were found to be 24.5 and 52.5% of the initial activity values for CDI and SOCl2 activated matrices, respectively. On the other hand the free enzyme lost its activity completely in 20 days. Immobilization, storage stability and repeated use capability experiments carried out in the presence of Ca2+ ions demonstrated higher stability, such as SOCl2 immobilized enzyme retained 83.7% and CDI immobilized enzyme retained 90.3% of the original activity of the enzyme. The immobilized enzymes that were used 20 times in 3 days in repeated batch experiments demonstrated that, in the absence of Ca2+ ions about 75% and in the presence of Ca2+ ions greater than 90% of the original enzyme activity was retained.

Covalent immobilization of alpha-amylase onto pHEMA microspheres: preparation and application to fixed bed reactor

Microspheres of poly(2-hydroxyethyl methacrylate) with and without cross-linker were prepared by suspension polymerization. As the amount of cross-linker increased, the equilibrium water content, enzyme loading, immobilization efficiency and recovered activity were all adversely affected. Enzyme alpha-amylase was immobilized onto the microspheres after activation with epichlorohydrin. The Km value for the immobilized enzyme (0.90% w/v) was much greater than that of the free enzyme (0.53% w/v). It was found that the inactivation constant (ki) increased from 2.23 x 10(-8) min-1 at 20 degrees C to 1.45 x 10(-4) min-1 at 60 degrees C. Since the enzyme activity increased as the temperature increased, the temperature profile yielded a peak at 50 degrees C. For free enzyme this is at 45 degrees C. The residence time was proportional to the percentage hydrolysis until a residence time of 12 min was reached. Beyond this the activity increase could not match the increase in residence time. The pH profile yielded a broadening upon immobilization in addition to a small shift to higher pH (from 5.5 to 6.0). The continuous run at 30 degrees C, 1.0% w/v starch concentration and flow rate of 40 cm3 h-1 led to only 20% loss in activity after a 120 h operation.