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In this study, immobilization of laccase (L) enzyme on magnetite (Fe 3 O 4 ) nanoparticles was achieved, so that the immobilized enzyme could be used repeatedly. For this purpose, Fe 3 O 4 nanoparticles were coated and functionalized with chitosan (CS) and laccase from Trametes versicolor was immobilized onto chitosancoated magnetic nanoparticles (Fe 3 O 4 -CS) by adsorption or covalent binding after activating the hydroxyl groups of chitosan with carbodiimide (EDAC) or cyanuric chloride (CC). For chitosan-coated magnetic nanoparticles, the thickness of CS layer was estimated as 1.0-4.8 nm by TEM, isoelectric point was detected as 6.86 by zeta (f)-potential measurements, and the saturation magnetization was determined as 25.2 emu g À1 by VSM, indicating that these nanoparticles were almost superparamagnetic. For free laccase and immobilized laccase systems, the optimum pH, temperature, and kinetic parameters were investigated; and the change of the activity against repeated use of the immobilized systems were examined. The results indicated that all immobilized systems retained more than 71% of their initial activity at the end of 30 batch uses.

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In this study, glucose isomerase enzyme was entrapped into modified and nonmodified calcium alginate gel beads. Various characteristics of free and immobilized enzymes such as the optimum pH, temperature and dependence of activity on storage and operational stability were evaluated. The optimum pH and temperature of free and immobilized glucose isomerase were found to be the same values as 7.5 and 60C, respectively. For free and immobilized enzymes, kinetic parameters were calculated as 1.79 ¥ 10 -2 and 8.27 ¥ 10 -3 mol/L for K m , and 2.39 ¥ 10 -3 and 6.03 ¥ 10 -3 mol/L min for V max , respectively. After 42 days of storage at 4C, free enzyme retained 56% of its initial activity, while for the immobilized enzyme, this value was observed as 86%. The immobilized samples were used repeatedly 22 times by retaining more than 85% of their initial activity. 4 Corresponding 234 PRACTICAL APPLICATIONSGlucose isomerase (GI) serves as an interesting model for studying structure-function relationships by advanced biochemical and genetic engineering techniques. Besides its academic importance, it has received increased attention by industries for its use in producing high-fructose corn syrup (HFCS) and for its potential application in the production of ethanol from hemicelluloses. The use of GI is expensive because it is an intracellular enzyme, and large quantities are needed to compensate for the high K m for glucose. Therefore, it is important to immobilize GI for its industrial applications. Recently, several methods for immobilizing GI have been developed. However, only a few are economical and yield enzyme preparations with properties that are suitable for commercial production of HFCS and ethanol.