title: Steering the enzymatic activity of proteins by ionic liquids. A case study of the enzyme kinetics of yeast alcohol dehydrogenase.
abstract: We explore ion-specific effects exerted by ionic liquids (ILs) on the enzyme kinetics of yeast alcohol dehydrogenase. The Michaelis-Menten reaction scheme is used to parameterize the observed kinetics in terms of the apparent dissociation constant of the substrate (Michaelis-Menten constant) K(M), the turnover number k(cat), which reflects the number of product molecules per enzyme molecule per second, and the enzymatic efficiency k(cat)/K(M) of the reaction. Results for fifteen salts are used to deduce Hofmeister anion and cation series. The ion rankings derived from K(M), k(cat) and k(cat)/K(M) differ markedly. Only the results for the enzymatic efficiency correspond to expectations from other phenomena, such as the thermal stability of native proteins. Anion variation has a significantly larger effect on the enzymatic efficiency than cation variation. All ILs decrease k(cat) relative to its value for the IL-free solution, thus driving enzyme deactivation. Enhancements of the enzymatic efficiency by some ions are founded in their effects on the Michaelis-Menten constant. The observed Hofmeister anion and cation series point toward hydrophobic interactions as an important factor controlling ion-specific effects on the enzymatic activity.
authors.affiliation: Physical Chemistry II, Faculty of Chemistry and Biochemistry, Ruhr-University Bochum, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Weibels
authors.forename: Adrian
authors.initials: A
authors.lastname: Syguda
authors.forename: Christian
authors.initials: C
authors.lastname: Herrmann
authors.forename: Hermann
authors.initials: H
authors.lastname: Weingärtner
mesh_terms: D000426:Alcohol Dehydrogenase / Q000737:chemistry / Q000378:metabolism*; D004789:Enzyme Activation; D052578:Ionic Liquids / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D012441:Saccharomyces cerevisiae / Q000201:enzymology*
chemical_list: D052578:Ionic Liquids; D000426:Alcohol Dehydrogenase