Surface-Functionalized Hyperbranched Poly(Amido Acid) Magnetic Nanocarriers for Covalent Immobilization of a Bacterial ?-Glutamyltranspeptidase

Abstract

In this study, we synthesized water-soluble hyperbranched poly(amido acid)s (HBPAAs) featuring multiple terminal CO2H units and internal tertiary amino and amido moieties and then used them in conjunction with an in situ Fe2+/Fe3+ co-precipitation process to prepare organic/magnetic nanocarriers comprising uniformly small magnetic iron oxide nanoparticles (NP) incorporated within the globular HBPAAs. Transmission electron microscopy revealed that the HBPAA-?-Fe2O3 NPs had dimensions of 6-11 nm, significantly smaller than those of the pristine ?-Fe2O3 (20-30 nm). Subsequently, we covalently immobilized a bacterial ?-glutamyltranspeptidase (BlGGT) upon the HBPAA-?-Fe2O3 nanocarriers through the formation of amide linkages in the presence of a coupling agent. Magnetization curves of the HBPAA-?-Fe2O3/BlGGT composites measured at 300 K suggested superparamagnetic characteristics, with a saturation magnetization of 52 emu g-1. The loading capacity of BlGGT on the HBPAA-?-Fe2O3 nanocarriers was 16 mg g-1 support; this sample provided a 48% recovery of the initial activity. The immobilized enzyme could be recycled 10 times with 32% retention of the initial activity; it had stability comparable with that of the free enzyme during a storage period of 63 days. The covalent immobilization and stability of the enzyme and the magnetization provided by the HBPAA-?-Fe2O3 NPs suggests that this approach could be an economical means of depositing bioactive enzymes upon nanocarriers for BlGGT-mediated bio-catalysis. © 2014 by the authors; licensee MDPI, Basel, Switzerland.