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    Immobilization of glucoamylase onto activated pHEMA/EGDMA microspheres: properties and application to a packed-bed reactor
    (Elsevier Science Inc, 1998) Arica, MY; Alaeddinoglu, NG; Hasirci, V
    Glucoamylase was covalently immobilized onto pHEMA/EGDMA microspheres of two different sizes: 50-100 mu m and 100-200 mu m in diameter. The activity of the enzyme on smaller microspheres was found to be almost twice that of the larger microspheres. A higher enzyme lending was observed on small microspheres (0.64 mg g(-1) support) as compared to large spheres (0.40 mg g(-1) support). The K-m of glucoamylase was significantly increased (approximately five times) upon immobilization, indicating decreased affinity by the enzyme for its substrate. V-max of the enzyme was, however, not as significantly altered upon immobilization as the K-m. More significantly, the V-max was much higher with the large substrate (dextrin) than it was with the small substrate (maltose). Activity of the immobilized enzyme was quite stable. In 120 h, only 9.0% of the immobilized glucoamylase activity was lost. (C) 1998 Elsevier Science Inc.
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    Invertase immobilized on spacer-arm attached poly(hydroxyethyl methacrylate) membrane: Preparation and properties
    (John Wiley & Sons Inc, 2000) Arica, MY; Senel, S; Alaeddinoglu, NG; Patir, S; Denizli, A
    Microporous poly(2-hydroxyethyl methacrylate) (pHEMA) membrane was prepared by UV-initiated photopolymerization. The spacer arm (i.e., hexamethylene diamine) was attached covalently and then invertase was immobilized by the condensation reaction of the amino groups of the spacer arm with carboxyl groups of the enzyme in the presence of carbodiimides. The values of the Michael's constant K-m of invertase were significantly larger (ca. 2.5 times) upon immobilization, indicating decreased affinity by the enzyme for its substrate, whereas V-max was smaller for the immobilized invertase. Immobilization improved the pH stability of the enzyme as well as its temperature stability. Thermal stability was found to increase with immobilization and at 70 degrees C the half times for the activity decay were 12 min for the free enzyme and 41 min for the immobilized enzyme. The immobilized enzyme activity was found to be quite stable in repeated experiments. (C) 2000 John Wiley & Sons, Inc.