Immobilization of glucose oxidase: A comparison of entrapment and covalent bonding

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Abstract
Glucose oxidase was immobilized onto poly(2‐hydroxyethyl methacrylate) (pHEMA) membranes by two methods: by covalent bonding through epichlorohydrin and by entrapment between pHEMA membranes. The highest immobilization efficiency was found to be 17.4% and 93.7% for the covalent bonding and entrapment, respectively. The Km values were 5.9 mmol dm−3, 8.8 mmol dm−3 and 12.4 mmol dm−3 for free, bound and entrapped enzyme, respectively. The Vmax values were 0.071 mmol dm−3 min−1, 0.067 mmol dm−3 min−1 and 0.056 mmol dm−3 min−1 for free, bound and entrapped enzyme. When the medium was saturated with oxygen, Km was not significantly altered but Vmax was. The optimum pH values for the free, covalently‐bound and entrapped enzyme were determined to be 5, 6, and 7, respectively. The optimum temperature was 30°C for free or covalently‐bound enzyme but 35°C for entrapped enzyme. The deactivation constant for bound enzyme was determined as 1.7 × 10−4 min−1 and 6.9 × 10−4 min−1 for the entrapped enzyme.