Effects of Structural Difference of Ionic Liquids on the Catalysis of Horseradish Peroxidase
2009
Hong, E.S., SK Chemicals, Ulsan, Republic of Korea | Park, J.H., University of Ulsan, Ulsan, Republic of Korea | Yoo, I.K., University of Ulsan, Ulsan, Republic of Korea | Ryu, K.G., University of Ulsan, Ulsan, Republic of Korea
The dependence of the catalytic properties of horseradish peroxidase on the structural changes of ionic liquids was investigated with two water-miscible ionic liquids, N-butyl-3-methypyridinium tetrafluoroborate ([BMP∧y][BF₄]) and 1-butyl-3-methylimidazolium methylsulfate ([BMIM][MeSO₄]), each of which shares an anion (BF₄-) or a cation (BMIM+) with 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]), respectively. The oxidation of guaiacol (2-methoxyphenol) with H₂O₂ was used as a model reaction. In order to minimize the effect of solution viscosity on the kinetic constants of the enzymatic catalysis, the enzymatic reactions for the kinetic study were performed in water-ionic liquid mixtures containing 25% (v/v) ionic liquid at maximum. Similarly to the previously reported results for [BMIM][BF₄], as the concentration of [BMP∧y][BF₄] increased, the K∧m value increased with a decrease in the k∧cat value: the K∧m value increased markedly from 2.8 mM in 100% water to 12.6 mM in 25% (v/v) ionic liquid, indicating that ionic liquid significantly weakens the binding affinity of guaiacol to the enzyme. On the contrary, [BMIM][MeSO₄] decreased the K∧m value to 1.4 mM in 25% (v/v) ionic liquid. [BMIM][MeSO₄] also decreased k∧cat more than 3-folds [from 13.8 s-¹ in 100% water to 4.1 s-¹ in 25% (v/v) ionic liquid]. These results indicate that the ionic liquids interact with the enzyme at the molecular level as well as at a macroscopic thermodynamic scale. Specifically, the anionic component of the ionic liquids influenced the catalysis of horseradish peroxidase in different ways.
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