Immobilization of glucose oxidase: a comparison of entrapment and covalent bonding.

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 degrees C for free or covalently-bound enzyme but 35 degrees C for entrapped enzyme. The deactivation constant for bound enzyme was determined as 1.7 x 10(-4) min-1 and 6.9 x 10(-4) min-1 for the entrapped enzyme.