Effects of Two Different Ionic Liquids , [ BMPy ][ BF 4 ] and [ BMIM ][ MeSO 4 ], on the Kinetics of Horseradish Peroxidase

Abstract

The effect of two water-miscible ionic liquids, 1-butyl-3-methypyridinuim tetrafluoroborate ([BMPy][BF(4)]) and 1-butyl-3-methylimidazolium methylsulfate ([BMIM][MeSO(4)]), on the horseradish peroxidase-catalyzed oxidation of 2-methoxyphenol (guaiacol) with hydrogen peroxide (HRP) was investigated. In order to minimize the effect of solution viscosity on the kinetic constants of HRP catalysis, the enzymatic reactions for the kinetic study were performed in water-ionic liquid mixtures containing 25% (v/v) ionic liquid at maximum. As the concentration of [BMPy][BF4] increased, the Km value increased with a slight decrease in the k(cat) value for the,oxidation of guaiacol by HRP: The Km 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 HIM. On the contrary, as the concentration of [BMIM][MeSO(4)] increased, the K, value decreased to 1.4 mM in 25% (v/v) ionic liquid. [BMIM][MeSO(4)] also decreased k(cat) 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 thermodynamic macroscopic scale.