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    Horseradish Peroxidase Immobilized onto Mesoporous Magnetic Hybrid Nanoflowers for Enzymatic Decolorization of Textile Dyes: A Highly Robust Bioreactor and Boosted Enzyme Stability
    (Amer Chemical Soc, 2024) Bakar, Busra; Akbulut, Mustafa; Ulusal, Fatma; Ulu, Ahmet; Ozdemir, Nalan; Ates, Burhan
    Recently, hybrid nanoflowers (hNFs), which are accepted as popular carrier supports in the development of enzyme immobilization strategies, have attracted much attention. In this study, the horseradish peroxidase (HRP) was immobilized to mesoporous magnetic Fe3O4-NH2 by forming Schiff base compounds and the HRP@Fe3O4-NH2/hNFs were then synthesized. Under optimal conditions, 95.0% of the available HRP was immobilized on the Fe3O4-NH2/hNFs. Structural morphology and characterization of synthesized HRP@Fe3O4-NH2/hNFs were investigated. The results demonstrated that the average size of HRP@Fe3O4-NH2/hNFs was determined to be around 220 nm. The zeta-potential and magnetic saturation values of HRP@Fe3O4-NH2/hNFs were -33.58 mV and similar to 30 emu/g, respectively. Additionally, the optimum pH, optimum temperature, thermal stability, kinetic parameters, reusability, and storage stability were examined. It was observed that the optimum pH value shifted from 5.0 to pH 8.0 after immobilization, while the optimum temperature shifted from 30 to 80 degrees C. K-m values were calculated to be 15.5502 and 7.6707 mM for free HRP and the HRP@Fe3O4-NH2/hNFs, respectively, and V-max values were calculated to be 0.0701 and 0.0038 mM min(-1). The low K-m value observed after immobilization indicated that the affinity of HRP for its substrate increased. The HRP@Fe3O4-NH2/hNFs showed higher thermal stability than free HRP, and its residual activity after six usage cycles was approximately 45%. While free HRP lost all of its activity within 120 min at 65 degrees C, the HRP@Fe3O4-NH2/hNFs retained almost all of its activity during the 6 h incubation period at 80 degrees C. Most importantly, the HRP@Fe3O4-NH2/hNFs demonstrated good potential efficiency for the biodegradation of methyl orange, phenol red, and methylene blue dyes. The HRP@Fe3O4-NH2/hNFs were used for a total of 8 cycles to degrade methyl orange, phenol red, and methylene blue, and degradation of around 81, 96, and 56% was obtained in 8 h, respectively. Overall, we believe that the HRP@Fe3O4-NH2/hNFs reported in this work can be potentially used in various industrial and environmental applications, particularly for the biodegradation of recalcitrant compounds, such as textile dyes.
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    Öğe
    L-asparaginase immobilized p(HEMA-GMA) cryogels: A recent study for biochemical, thermodynamic and kinetic parameters
    (Elsevier Sci Ltd, 2021) Noma, Samir Abbas Ali; Acet, Omur; Ulu, Ahmet; Onal, Burcu; Odabasi, Mehmet; Ates, Burhan
    Cryogels have recently been attracted intense attention as suitable carriers for enzyme immobilization. Herein, L-asparaginase was selected as the model enzyme due to its application such as pharmaceutical and food. Under optimum conditions, L-asparaginase was immobilized on poly (2-hydroxyethyl methacrylate-glycidyl methacrylate) cryogels with 68.8% of immobilization yield and 69.3% of activity recovery. The immobilized enzyme exhibited improved stability with respect to the soluble enzyme at extreme conditions, especially around acidic pH and high temperature. Also, the storage stability and reusability of the immobilized enzyme were found to be approximately 54% and 52% of the original activity after 28 days at room temperature and 10 cycles, respectively. The thermodynamic studies indicated that activation energy (E-a) of the free enzyme decreased from 13.08 to 10.97 kJ/mol, which means an increase in the thermostability of L-asparaginase. The Michaelis-Menten constants (K-m) of 2.04 and 1.67 mM, and the maximum reaction rates (V-max) of 170.0 and 115.0 mu M min(-1) were estimated for soluble and immobilized L-asparaginase, respectively. These findings demonstrated that the designed cryogels turn out to be a good carrier matrix for L-asparaginase immobilization with high catalytic efficiency and enhanced stability.