Enhanced Catalytic Stability of Laccase Immobilized on Copper Oxide Nanoparticles

Abstract

This study describe the design and catalytic activity of enzymatic nanoreactors based on copper oxide nanoparticles surface-functionalized with laccase (CuO-Lac) from Coriolopsis gallica. Transmission electron micrographs show complete laccase coverage on the nanoparticle surfaces. In addition, the catalytic rate (kcat) of the immobilized laccase is two-fold higher at an optimized pH, when compared with free laccase, while the affinity constant (KM) is not significantly affected. Importantly, the total turnover number (TNN) of the CuO-Lac nanoreactors reaches 358 ± 9 × 106 mol ABTS/mol laccase, which is four times higher than the TTN obtained for the free enzyme (88 ± 3 × 106). Thus, our nanoreactors exhibit a significant improvement in laccase catalytic performance. Inductively coupled plasma mass spectrometry was used to confirm the loss of copper ions from free laccase during the catalytic cycle, suggesting that the CuO nanoparticles act as a copper ion source that prevents enzyme inactivation. This work contributes to an improved understanding of the CuO-laccase interface and confirms that CuO nanoparticles serve as copper sources for laccase during catalysis.