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    Characterization of β-galactosidase immobilized into poly(hydroxyethylmethacrylate) membranes
    (Mbr Press Inc, 1998) Adali, O; Baran, T; Arica, MY
    beta-galactosidase was immobilized into pHEMA membranes with the highest specific activity yield of 9.5%. The specific activity of the entrapped enzyme was found to be decreased as the enzyme loading increased in pHEMA membranes. The optimum pH and temperature for maximum activity of the immobilized beta-galactosidase was found to be at pH 7.5 and 50 degrees C, respectively, and were the same as native enzyme. K-m and V-max values for the free enzyme were found to be 0.256 mM and 26.6 mu mole/min/mg, respectively. K-m value of immobilized beta-galactosidase was found to be increased about 3 folds upon immobilization. Operational, thermal and storage stability of beta-galactosidase were found to increase with immobilization. Immobilized enzyme preparation was reused in 15 cycles without significant loss in activity.
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    Comparison of β-galactosidase immobilization by entrapment in and adsorption on poly(2-hydroxyethylmethacrylate) membranes
    (John Wiley & Sons Ltd, 1997) Baran, T; Arica, MY; Denizli, A; Hasirci, V
    beta-Galactosidase was immobilized in/on poly(2-hydroxyethyl methacrylate) (pHEMA) membranes by two different methods: adsorption on Cibacron F3GA derivatized pHEMA membranes (pHEMA-CB), and entrapment in the bulk of the pHEMA membranes. The maximum beta-galactosidase adsorption on pHEMA-CB membranes was obtained as 95.6 mu g cm(-2) in 2.0 mg cm(-3) enzyme solution. The adsorption phenomena appeared to follow a typical Langmuir isotherm. In the entrapment, an increase in beta-galactosidase loading resulted in a consistent increase in membrane activity from 3.3 x 10(-2) to 17.8 x 10(-2) U cm(-2) pHEMA membranes. The K-m values for both immobilized beta-galactosidase (adsorbed 0.32 mM and entrapped 0.81 mM) were higher than that of the free enzyme (0.26 mM). The optimum reaction temperature of the adsorbed enzyme was 5 degrees C higher than that of both the free and the entrapped enzyme. The optimum reaction pH was 7.5 for free and both immobilized preparations. After 15 successive uses the retained activity of the adsorbed and the entrapped enzymes was 80% and 95%, respectively. The storage stability of the enzyme was found to increase upon immobilization.
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    Dye derived and metal incorporated affinity poly(2-hydroxyethyl methacrylate) membranes for use in enzyme immobilization
    (John Wiley & Sons Ltd, 1998) Arica, MY; Denizli, A; Baran, T; Hasirci, V
    Microporous poly(2-hydroxyethyl methacrylate) (PHEMA) membranes were prepared by W-initiated photopolymerization of HEMA in the presence of an initiator (alpha,alpha'-azobisisobutyronitrile, AIBN). An affinity dye Cibacron Blue F3GA (CB) was attached covalently and then Fe3+ ions incorporated. The PHEMA-CB and PHEMA-CB-Fe3+ membranes derived were used for adsorption of glucose oxidase (GOD). The adsorption capacities of these membranes were determined under conditions of different pH and with different concentrations of the adsorbate in the medium. The adsorption phenomena appeared to follow a typical Langmuir isotherm. The glucose oxidase adsorption capacity of the Fe3+ incorporated membrane (87 mu g cm(-2)) was greater than that of the dye-derived membrane (66 mu g cm(-2)). Non-specific adsorption of the glucose oxidase on the PHEMA membranes was negligible. The K-m values for both immobilized glucose oxidase PHEMA-CB-GOD (8.3) and PHEMA-CB-Fe3+-GOD (7.6) were higher than that of the free enzyme (6.2 mM). Optimum reaction pH was 5.5 for the free and 6.0 for both immobilized preparations. The optimum reaction temperature of the adsorbed enzymes was 5 degrees C higher than that of the free enzyme and was significantly broader. After 15 successive uses the retained activity of the adsorbed enzyme was 87%. It was observed that enzymes could be repeatedly adsorbed and desorbed on the derived PHEMA membranes without significant loss in adsorption capacity or enzymic activity. (C) 1998 SCI.
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    β-galactosidase immobilization into poly(hydroxyethyl methacrylate) membrane and performance in a continuous system
    (Wiley-Blackwell, 1999) Arica, MY; Baran, T; Denizli, A
    The activity of beta-galactosidase immobilized into a poly(2-hydroxyethyl methacrylate) (pHEMA) membrane increased from 1.5 to 10.8 U/g pHEMA upon increase in enzyme loading. The K-m values for the free and the entrapped enzyme were found to be 0.26 and 0.81 mM, respectively. The optimum reaction temperatures for the free and the entrapped beta-galactosidase were both found to be 50 degrees C. Similarly, the optimum reaction pH was 7.5 for both the free and the entrapped enzyme. The immobilized beta-galactosidase was characterized in a continuous system during lactose hydrolysis and the operational inactivation rate constant (k(iop)) of the entrapped enzyme was found to be 3.1 x 10(-5) min(-1). (C) 1999 John Wiley & Sons, Inc.