Immobilization of purified β-glucuronidase on ZnO nanoparticles for efficient biotransformation of glycyrrhizin in ionic liquid/buffer biphasic system

Purified recombinant β-glucuronidase (PGUS-E) from Aspergillus oryzae Li-3 was immobilized on the zinc oxide nanoparticles (ZnO-NP) for glycyrrhizin (GL) biotransformation. The optimal loading efficiency of the PGUS-E on ZnO-NP was 6.52U/mg with an average of 85.83% immobilization yield. The adsorption of the PGUS-E on ZnO-NP was confirmed using scanning electron microscope (SEM) and fourier transform infrared (FTIR) spectroscope. The comparative catalytic efficiency of the immobilized PGUS-E was evaluated in the ionic liquids (ILs) media and buffer. The higher catalytic efficiency of the immobilized PGUS-E was recorded in the hydrophobic ionic liquid [Bmim]PF6 (20% volumetric ratio) compared with other ILs media and pure buffer. The temperature and pH profiles of the immobilized PGUS-E were also determined for ionic liquid (ILs) media and pure buffer. The higher operational stability of the immobilized PGUS-E was observed in the IL co-solvent medium than the pure buffer medium; and after 8 repeated uses an average 30.54% and 7.42% of its catalytic activity was respectively retained. The recovery rate of the IL medium ([Bmim]PF6) was as high as 76.11%. The measurement of the enzyme kinetic parameters and activation energy also explicitly display the superiority of the IL co-solvent media over the monophasic media.