Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 14Citation - Scopus: 25Kinetic and Equilibrium Studies of Adsorption of Ss-Glucuronidase by Clinoptilolite-Rich Minerals(Elsevier Ltd., 2015) Demirbüker Kavak, Dilek; Ülkü, SemraThe adsorption of the bacterial β-glucuronidase (GUS) enzyme, which is thought to be responsible for the production of reactive metabolites related to some diseases and cancer development, by clinoptilolite-rich mineral was investigated. Batch experiments were performed to analyze of the effects of the clinoptilolite amount and particle size, initial GUS concentration, shaking rate, pH and temperature on the adsorption equilibrium and kinetics. Adsorption equilibrium data were interpreted in terms of Langmuir and Freundlich isotherms; and they were well represented by the Langmuir isotherm model. The percentage of GUS removal by the clinoptilolite-rich mineral was changed in the range of 9.4-54.4% depending on its initial concentration. The kinetic data were analyzed using external film diffusion, intraparticle diffusion, pseudo-first-order and pseudo-second-order models and both external film and intraparticle diffusion appeared to be effective in GUS adsorption. Thermodynamic studies indicated that GUS adsorption is exothermic, physical and spontaneous at the temperatures investigated (288-310 K)Article Citation - WoS: 42Citation - Scopus: 60Pistacia Terebinthus Extract: as a Potential Antioxidant, Antimicrobial and Possible Ss-Glucuronidase Inhibitor(Elsevier Ltd., 2010) Demirbüker Kavak, Dilek; Altıok, Evren; Bayraktar, Oğuz; Ülkü, SemraIn this study, inhibition of Escherichia coli glucuronidase (GUS) by a plant extract of Pistacia terebinthus was investigated. P. terebinthus (from Karaburun region in Turkey) leaf extract exhibits various bioactivities, such as antioxidant, antimicrobial and cytotoxic property because of its flavonoid, phenolic and alkaloid contents. HPLC analyses were performed to evaluate the composition of the extract and main flavonoid compounds such as luteolin, luteolin-7-glucoside and apigenin-7-glucoside were detected in extract. GUS activity and kinetic data of the GUS were obtained by measuring rate of production of resulting fluorescent 4-methylumbelliferone (4-MU) and phenolphthalein fluorometrically and spectrophotometrically, respectively. Plant leaves showed higher antioxidant capacity as 85 TEAC (trolox equivalent antioxidant capacity) value and higher antimicrobial activity towards Staphylococcus aureus. 92.4% GUS enzyme inhibition was achieved with 8.3 μg ml-1 crude extract concentration, where IC50 value was found as 2.1 (±0.2) μg ml-1. Kinetic studies by nonlinear regression revealed that inhibition type caused by plant extract was mixed type (noncompetitive and competitive together). Km and Vmax values were 96.94 ± 9.68 nM and 7.81 ± 0.16 nmol min-1 mg-1, respectively. Inhibition constant (αKi) was found as 7.00 ± 0.93 nM having α value 2.17 ± 0.93. Our results may provide useful information regarding the inhibition of microbial GUS activity, preventing deglucuronidation and reducing possible cancer risk by bioactive P. terebinthus crude extract. © 2010 Elsevier B.V. All rights reserved.