The development and evaluation of β-glucosidase immobilized magnetic nanoparticles as recoverable biocatalysts

Magnetic nanoparticle (MNP) solid core supports bound with beta-glucosidase (beta G) were evaluated as recyclable biocatalysts. To determine whether the relative positioning of immobilized beta G to MNP surfaces impacts enzyme activity, MNPs were conjugated with beta G using a glutaraldehyde cross-linker for proximal binding with different polyethylene glycol spacer-linkers (MW: 200, 400, 1000). MNP surface modifications were validated by X-ray photoelectron spectroscopy and the measurement of saturation magnetization for the bioconjugates revealed minor decreases in magnetic moments relative to core MNPs. All four bioconjugates showed similar binding efficiencies for beta G, but measured increases in K-m values and decreases in V-max values, regardless of the spacer length, indicated that the specific activity of beta G was lowered upon enzyme immobilization and spacer lengths were negligible. Despite a reduction in beta G activity, immobilization conferred thermal stability under conditions in which the native enzyme is inactivated. To evaluate the recycling properties of the bioconjugates, enzyme activity measurements were conducted for ten consecutive rounds at 45 degrees C. The bioconjugates hydrolyzed total amounts of p-nitrophenyl beta-D-glucoside comparable to a single application of unmodified beta G following the third recycling round along with significant activity after ten rounds. Based on these results, the enhanced stability of immobilized beta G on recoverable MNPs provides a means for reducing the amount of beta G required for cellulose hydrolysis, thereby reducing costs associated with ethanol production. (C) 2018 Elsevier B.V. All rights reserved.