In this study, a
novel enzyme immobilization method was developed
to enhance the catalytic stability of enzymes. In this strategy, ionic
liquid (IL) modified magnetic chitosan (MCS) composites were used
as supports for lipase adsorption and graphene oxide (GO) was employed
as shell coating for the first time. The modifier used was imidazolium-based
IL with a side alkyl chain which was composed of 8 −CH2 and a terminal hydroxyl group. The prepared supports IL-MCS,
immobilized lipase PPL-IL-MCS, and GO/PPL-IL-MCS were well characterized.
The GO shielding lipase GO/PPL-IL-MCS maintained high activity (2468
U/g), which was 6.72-fold of free lipase. In addition, the pH and
temperature effect on lipase activity were investigated. The thermal
stability, denaturants stability, storage stibility, and reusing stability
were also studied. Compared to PPL-IL-MCS, the stabilities of GO/PPL-IL-MCS
were all enhanced while keeping high activity. For example, after
10 cycles of reuse, the residual activity of GO/PPL-IL-MCS was 92.1%,
which was higher than that of 88.4% for PPL-IL-MCS. Furthermore, the
apparent K
m of PPL-IL-MCS and GO/PPL-IL-MCS
was 5.7 and 8.8 mg/mL, respectively, which were both lower than that
of PPL-MCS (17.1 mg/mL). Circular dichroism (CD) was used to analyze
the secondary structure of lipase to explain the mechanism of stable
enhancement of immobilized enzyme. This work demonstrated that GO
was used as a shell coating for the first time to improve the lipase
stability. This immobilization method provides a reference for the
immobilization of other kinds of enzymes.
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