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.
Jack bean urease (urea aminohydrolase, E.C. 3.5.1.5) was entrapped into chitosan-alginate polyelectrolyte complexes (C-A PEC) and poly(acrylamide-co-acrylic acid)/kappa-carrageenan (P(AAm-co-AA)/carrageenan) hydrogels for the potential use in immobilization of urease, not previously reported. The effects of pH, temperature, storage stability, reuse number, and thermal stability on the free and immobilized urease were examined. For the free and immobilized urease into C-A PEC and P(AAm-co-AA)/carrageenan, the optimum pH was found to be 7.5 and 8, respectively. The optimum temperature of the free and immobilized enzymes was also observed to be 55 and 60 degrees C, respectively. Michaelis-Menten constant (K(m)) values for both immobilized urease were also observed smaller than free enzyme. The storage stability values of immobilized enzyme systems were observed as 48 and 70%, respectively, after 70 days. In addition to this, it was observed that, after 20th use in 5 days, the retained activities for immobilized enzyme into C-A PEC and P(AAm-co-AA)/carrageenan matrixes were found as 55 and 89%, respectively. Thermal stability of the free urease was also increased by a result of immobilization.
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