Prediction and Experimental Validation of Co‐Solvent Influence on Michaelis Constants: A Thermodynamic Activity‐Based Approach. Issue 61 (12th October 2018)

• Record Type: Journal Article
• Authors: Wangler, Anton; Böttcher, Dominik; Hüser, Aline; Sadowski, Gabriele; Held, Christoph
• Is Part Of: Chemistry. Volume 24:Issue 61(2018)
• Page Start: 16418
• Page End: 16425
• Publication Date: 2018-10-12
• Subjects: acetophenone -- alcohol dehydrogenase -- enzymes -- ePC-SAFT -- kinetics; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201803573
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: Co‐solvents are known to influence the Michaelis constant K M of enzyme‐catalyzed reactions. In the literature, co‐solvent effects on K M are usually explained by interactions between enzyme and co‐solvent. Very recent works replaced substrate concentrations with thermodynamic activities to separate enzyme–co‐solvent from substrate–co‐solvent interactions This yields the thermodynamic‐activity‐based Michalis constant K M a . In this work, this approach was extended to alcohol dehydrogenase (ADH)‐catalyzed reduction of acetophenone (ACP), a two‐substrate reaction. It was experimentally found that polyethylene glycol (PEG) 6000 increased K M of ACP and decreased K M of nicotinamide adenine dinucleotide (NADH). To predict K M a values, non‐covalent interactions between substrates and reaction media were taken into account by electrolyte perturbed‐chain statistical associating fluid theory (ePC‐SAFT) modelling. In contrast to experimental K M values, their activity‐based pendants K M a were independent of co‐solvent. To further verify the approach, the reduction of 2‐pentanone catalyzed by the same ADH was investigated. Interestingly, the addition of PEG caused a decrease of both K M of 2‐pentanone and K M of NADH. Based on K M a values obtained from K M in co‐solvent‐free conditions and activity coefficients from ePC‐SAFT, the influence of the co‐solvent on K M was quantitatively predicted. Thus, the approach known for pseudo one‐substrate reactions was successfully transferred to two‐substrate reactions. Furthermore, the advantage of thermodynamic activities over concentrations in the field of enzyme kinetics is highlighted. Abstract : Co‐solvent effect : A thermodynamic‐activity‐based approach renders quantitatively predictable Michaelis constants for enzyme‐catalyzed two‐substrate reactions. Co‐solvent–enzyme interactions were proven to play a minor role in the effect of co‐solvents on Michaelis constants. The approach will help to gain new insights on co‐solvent‐substrate‐enzyme interactions.