Immobilization, stability and enzymatic activity of albumin and trypsin adsorbed onto nanostructured mesoporous SBA-15 with compatible pore sizes

Abstract

Albumin and trypsin were immobilized in the interior of SBA-15 mesochannels having suitable pore sizes through adsorptive binding. SBA-15's with different pore sizes (47 and 55 Å) were synthesized and the effects of factors such as temperature, pH and ionic strength were investigated on loading efficiency and bioactivity. Maximal loading for albumin (8.3 μmol g⁻¹ SBA-15) and trypsin (23.5 μmol g⁻¹ SBA-15) were achieved after 24 hours mixing at room temperature. Increasing the temperature during mixing increased the albumin loading to 9.9 μmol g⁻¹ SBA-15 at 45 °C after 24 h incubation, while the loading of trypsin was decreased. The N₂ adsorption–desorption isotherms of synthesized and immobilized proteins were obtained to ensure that the protein immobilization was occurred inside the channels of the supports. The activity of adsorbed trypsin was measured at different temperatures to investigate its thermal stability. The proteolytic stability of adsorbed trypsin against α-chymotrypsin was also studied. The kinetic constants (K_m and V_max) of the adsorbed trypsin were determined and compared with the soluble enzyme. The results indicated that the adsorbed trypsin retained 42% of its activity after 2 hours incubation at 45 °C and also retained 98 percent of its activity after chymotryptic treatment. This increased thermal and proteolytic stability could compensate the decrease in the affinity (higher K_m) of the adsorbed enzyme toward the substrate and its lower maximum velocity.