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Öğe Dye-affinity hollow-fibres and their lysozyme adsorption-desorption characteristics(John Wiley & Sons Ltd, 2001) Şenel, S.; Akgöl, S.; Arica, Y.; Denizli, A.Dye-affinity adsorption is increasingly used for protein separation. Hollow-fibres have advantages as adsorbents in comparison to conventional bead supports because they are not compressible and can eliminate internal diffusion limitations. The aim of this study was to explore in detail the performance of polyamide hollow-fibres to which Reactive Green HE-4BD was attached for adsorption of lysozyme. The hollow-fibre was characterized by scanning electron microscopy. These dye-carrying hollow-fibres (26.3 mu mol g(-1)) were used in the lysozyme adsorption-elution studies. The effect of initial concentration of lysozyme and medium pH on the adsorption efficiency of dye-attached hollow-fibres was studied in a batch system. The non-specific adsorption of lysozyme on the polyamide hollow-fibres was 1.8 mgg(-1). Reactive Green HE-4BD attachment significantly increased the lysozyme adsorption up to 41.1 mgg(-1). Langmuir adsorption model was found to be applicable in interpreting lead adsorption by Reactive Green HE-4BD attached hollow fibres. Significant amount of the adsorbed lysozyme (up to 95%) was eluted in lh in the elution medium containing 1.0M NaSCN at pH 8.0. In order to determine the effects of adsorption conditions on possible conformational changes of lysozyme structure, fluorescence spectrophotometry was employed. We concluded that polyamide dye-affinity hollow-fibres can be applied for lysozyme adsorption without causing any significant conformational changes. Repeated adsorption-elution processes showed that these dye-attached hollow-fibres are suitable for lysozyme adsorption. (C) 2001 Society of Chemical Industry.Öğe Hydrolysis of sucrose by invertase immobilized onto novel magnetic polyvinylalcohol microspheres(Elsevier Sci Ltd, 2001) Akgöl, S.; Kaçar, Y.; Denizli, A.; Arıca, M.Y.The magnetic polyvinylalcohol (PVAL) microspheres were prepared by crosslinking glutaraldehyde. 1,1 ' -Carbonyldiimidazole (CDI), a carbonylating agent was used for the activation of hydroxyl groups of polyvinylalcohol, and invertase immobilized onto the magnetic PVAL microspheres by covalent bonding through the amino group. The retained activity of the immobilized invertase was 74%. Kinetic parameters were determined for immobilized invertase, as well as for the free enzyme. The K-m values for immobilized invertase (55 mM sucrose) were higher than that of the free enzyme (24 mM sucrose), whereas V-max values were smaller for the immobilized invertase. The optimum operational temperature was 5 degreesC higher for immobilized enzyme than that of the free enzyme. The operational inactivation rate constant (k(opi)) of the immobilized invertase at 35 degreesC with 200 mM sucrose was 5.83 x 10(-5) min(-1). Thermal and storage stabilities were found to increase with immobilization. (C) 2001 Elsevier Science Ltd. All rights reserved.Öğe Immobilization of catalase via adsorption onto L-histidine grafted functional pHEMA based membrane(Elsevier Science Bv, 2001) Akgöl, S.; Kacar, Y.; Özkara, S.; Yavuz, H.; Denizli, A.; Arica, M.Y.Poly(2-hydroxyethylmethacrylate) (pHEMA) based flat sheet membrane was prepared by UV-initiated photopolymerization technique. The membrane was then grafted with L-histidine. Catalase immobilization onto the membrane from aqueous solutions containing different amounts of catalase at different pH was investigated in a batch system. The maximum catalase immobilization capacity of the pHEMA-histidine membrane was 86 mug cm(-2). The activity yield was decreased with the increase of the enzyme loading. It was observed that there was a significant change between V-max value of the free catalase and V-max value of the adsorbed catalase on the pHEMA-histidine membrane. The K-m value of the immobilized enzyme was higher 1.5 times than that of the free enzyme. Optimum operational temperature was 5 degreesC higher than that of the free enzyme and was significantly broader. It was observed that enzyme could be repeatedly adsorbed and desorbed without loss of adsorption capacity or enzyme activity. (C) 2001 Elsevier Science B.V. All rights reserved.Öğe Poly(hydroxyethyl methacrylate-co-glycidyl methacrylate) reactive membrane utilised for cholesterol oxidase immobilisation(John Wiley & Sons Ltd, 2002) Akgöl, S.; Bayramoğlu, G.; Kaçar, Y.; Denizli, A; Arıca, M.Y.Poly(2-hydroxyethyl methacrylate-co-glycidyl methacrylate) p(HEMA-GMA) membrane was prepared by UV-initiated photopolymerisation of 2-hydroxyethyl methacrylate (HEMA) and glycidyl methacrylate (GMA) in the presence of an initiator, azobisisobutyronitrile (AIBN). Cholesterol oxidase was immobilised directly on the membrane by forming covalent bonds between its amino groups and the epoxide groups of the membrane. An average of 53 mug of enzyme was immobilised per cm(2) of membrane, and the bound enzyme retained about 67% of its initial activity. Immobilisation improved the pH stability of the enzyme as well as its temperature stability. The optimum temperature was 5degreesC higher than that of the free enzyme and was significantly broader. The thermal inactivation rate constants for free and immobilised preparations at 70degreesC were calculated as k(i (free)) 1.06 x 10(-1) min(-1) and k(i (imm)) 2.68 x 10(-2) min(-1), respectively. The immobilised enzyme activity was found to be quite stable in the repeated experiments. (C) 2002 Society of Chemical Industry.
