Immobilization of recombinant l-asparaginase from Geobacillus kaustophilus on magnetic MWCNT-nickel composites

In this study, L-asparaginase from thermophilic Geobacillus kaustophilus was heterologously expressed in Escherichia coli and purified by 6.14-fold using Ni-NTA column. The purified GkASNase was immobilized covalently on newly developed magnetic nickel/nickel oxide multi-walled carbon nanotubes particles modified with 3-aminopropyltriethoxysilane or (3-glycidoxypropyl) trimethoxysilane. The results of biochemical characterizations of free and immobilized L-asparaginase samples showed that the optimum pH was 8.5 for all the L-asparaginase samples. However, the optimum temperature was found to be 55 °C for the free enzyme, while the immobilized L-asparaginase samples had an optimum temperature at 60 °C. The thermal inactivation experiments showed that the thermal stability of immobilized L-asparaginase preparations increased at least 40 folds at 60 °C compared to the free enzyme. The both immobilized L-asparaginase preparations remained at least 90 % of their initial activities after 10 reuses. The acrylamide formation was reduced 100 % by the both immobilized L-asparaginase preparations in 60 min, whereas the corresponding value was 98 % for the free enzyme. The results showed that the covalent immobilization of L-asparaginase on modified nickel/nickel oxide multi-walled carbon nanotubes resulted in the obtention of ease of separable, thermally stable, reusable and more effective L-asparaginase preparations in the mitigation of acrylamide compared to free counterpart.