Abstract
Biomineralized uniform and well-organized calcium carbonate microspheres were synthesized for enzyme immobilization, and the immobilized enzyme was successfully stabilized. The physicochemical parameters of calcium carbonate were studied using scanning electron microscopy with energy-dispersive X-ray spectroscopy, particle size analysis, X-ray diffraction analysis, Fourier-transform infrared spectroscopy, and surface area measurement. Additionally, Barrett-Joyner-Halenda adsorption/desorption analysis showed that the calcium carbonate microspheres provided efficient mesopore space for enzyme loading. As a model enzyme, carboxyl esterase (CE) was entrapped and then cross-linked to form an enzyme structure. In this aggregate, the cross-linked enzymes cannot leach out from mesopores, resulting in enzyme stability. The hydrolytic activities of the free and cross-linked enzymes were analyzed over broad temperature and pH ranges. The cross-linked enzyme displayed better activity than the free enzyme. Furthermore, the immobilized CE was found to be stable for more than 30 days, preserving 60% of its initial activity even after being reused more than 10 times. This report is expected to be the first demonstration of a stabilized cross-linked enzyme system in calcium carbonate microspheres, which can be applied in enzyme catalyzed reactions involved in bioprocessing, bioremediation, and bioconversion.
Highlights
Enzymes are proteins that catalyze chemical reactions, reducing the initial energy input, by increasing the reaction rate
The particle size analysis obtained by particle size analyzer (PSA), showing 5.5 ± 1.8 μm size distribution (Figure 2B), and Energy-dispersive X-ray spectroscopy (EDS) was used to confirm CaCO3 surface (Figure 2C)
The X-ray diffraction (XRD) patterns of particle confirmed that well-crystallized mixed vaterite and aragonite phase, with their characteristic diffraction peaks of 2θ values at about 25.4 (1 0 1), 37.9 (0 0 4), 48.2 (2 0 0), 54.0 (1 0 5), 55.1 (2 1 1), and 62.9 (2 0 4), indicating nature of the calcium carbonate, were obtained (Figure 2D)
Summary
Enzymes are proteins that catalyze chemical reactions, reducing the initial energy input, by increasing the reaction rate. Based on enzyme processes relevant to environment-friendly features used in chemical transformation, enzymes are widely utilized in various fields such as food, pharmaceuticals, biodiesel, and biofuels (Datta et al, 2013; Hwang and Gu, 2013; Jesionowski et al, 2014). Industrial applications of enzymes are increasing (Schoemaker et al, 2003). Free enzymes are destabilized, and it is difficult to reuse them efficiently (Iyer and Ananthanarayan, 2008). Immobilization of an enzyme can prevent it from structural denaturation caused by the external environment; enzyme activity can be maintained from various reaction conditions by preserving storage stability
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