Exploring Michaelis–Menten Kinetics and the Inhibition of Catalysis in a Synthetic Mimic of Catechol Oxidase: An Experiment for the Inorganic Chemistry or Biochemistry Laboratory

Abstract

This report describes a laboratory experiment for an undergraduate-level inorganic chemistry or biochemistry course involving the study of the kinetics of the catecholase activity of a synthetic nickel(II)–oximate complex. A model substrate, 3,5-di-tert-butylcatechol (DBC), undergoes aerobic oxidation to 3,5-di-tert-butylbenzoquinone (DBQ) in the reaction. Students determine the initial rates of production of DBQ, measured by the increase of the absorption in the UV–vis spectrum at 400 nm; this was performed for solutions containing five separate substrate-to-catalyst ratios. Saturation kinetics was observed at high substrate-to-catalyst ratios, and the Michaelis–Menten model of enzymatic kinetics was applied to determine the kinetic parameters for the catalyst (kcat, Vmax, and Km). Students explored the ability of two antioxidants, l-glutathione and α-tocopherol, to inhibit the oxidation reaction. The experiment has been employed at a small, four-year college in the Inorganic Chemistry course for three semesters. The experiment successfully provided students with a hands-on experience of using spectroscopy to monitor the kinetics of an enzyme-like system, including producing relevant plots and data analysis of Michaelis–Menten kinetic parameters. Students also examined the effects and roles of antioxidants in biochemical systems.