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Phthalate Esters Degradation Mechanisms by Enzymes
(01. Izmir Institute of Technology, 2023) Balcı, Esin; Sofuoğlu, Aysun; Mohamed, Gülşah Şanlı
Phthalate esters (PAEs) stand out as the priority toxicants due to their carcinogenic, mutagenic, and teratogenic properties. The enzymatic degradation is hailed for its recognized safe and environmentally friendly properties. This study delved into PAEs' degradation, especially dibutyl phthalate (DBP) and diethylhexyl phthalate (DEHP) by recombinant esterase from Geobacillus sp. isolated from Balçova Geothermal region in İzmir. The esterase exhibited efficient degradation of DBP but had limited effectiveness in degrading DEHP. Many experiments were conducted to compare the ability of recombinant esterase to degrade DBP and DEHP with that of commercially available enzymes secreted from various microorganisms. Among these enzymes, Bacillus subtilis esterase and Rhizomucor miehei lipase had the highest ability. They were immobilized on halloysite nanotubes (HNTs) by adsorption method to enhance their stability and prolong their activity in applications. To investigate the impact of immobilization methods, two bionanocomposites were formed by immobilization of Bacillus subtilis esterase to HNTs with chitosan (CTS) and alginate (ALG) by the cross-linking method. Two fixed-bed reactors with CTS-HNT-EST and ALG-HNT-EST were operated in batch and continuous modes for PAEs' degradation. CTS-HNT-EST exhibited superior efficacy and durability in PAEs' removal for both modes. Lastly, bioremediation experiments were conducted in PAEs-contaminated soils using Bacillus subtilis esterase and recombinant esterase. Although both esterase had the same active site triad, recombinant esterase had a less significant effect on PAEs' degradation. This fact can be attributed to different substrate specificity and enzyme dynamics. Despite variations in their degradation capabilities, both commercial and newly engineered recombinant enzymes demonstrate considerable potential for breaking down PAEs.
Preparation of Tyrosinase Immobilized Chitosan and Gelatin Films for Detection of Parathion-Methyl
(Izmir Institute of Technology, 2012) Polatoğlu, İlker; Çakıcıoğlu Özkan, Seher Fehime
In this work, tyrosinase immobilized chitosan and gelatin films as optical enzyme sensors which were characterized and optimized by UV spectrophotometer, were developed for detection of the pesticide parathion-methyl. The results show that the best sensor was the chitosan supported ones (TCA) prepared by adsorption method due to higher responsiveness and higher catalytic activity. The prepared sensors used for 10 times without significant loss in activity indicate good operational stability. Immobilization of the enzyme to chitosan support increases the pH, temperature and storage stability with respect to free enzyme due to providing structural rigidity and appropriate flexibility by immobilization. The other indication is that, isopropyl alcohol is the most appropriate organic solvent to solve the pesticide due to showing higher solubility for parathion-methyl and lowest inhibition (decrease in activity) for the enzyme. TCA has wide linear detection range and it can detect the parathion methyl concentration below the Maximum Residue Limit (MRL). The decrease in enzyme activity was obtained up to 10 mg/l (ppm) parathion-methyl concentration. The other result is that, kinetics of the immobilized enzyme was reaction controlled for higher substrate concentrations as understood from effectiveness factor, η. Atomic force microscopy (AFM) and FTIR analysis show that tyrosinase enzyme was successfully coated on the surface of chitosan and gelatin films. After using the optical enzyme sensor the binding of product o-quinone to chitosan and gelatin films were observed which was characterized by AFM results and the UV visible absorption peaks.

Phd Degree / Doktora

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