Review Questions in the Chemical Enzymology of MAO Rona R. Ramsay 1,* and Alen Albreht 2 1 Biomedical Sciences Research Complex, School of Biology, University of St Andrews, St Andrews KY16 9ST, UK 2 Laboratory for Food Chemistry, Department of Analytical Chemistry, National Institute of Chemistry, Hajdrihova 19, SI-1000 Ljubljana, Slovenia;
[email protected] * Correspondence:
[email protected]; Tel.: +44-(0)-1334-474740 Abstract: We have structure, a wealth of kinetic data, thousands of chemical ligands and clinical information for the effects of a range of drugs on monoamine oxidase activity in vivo. We have comparative information from various species and mutations on kinetics and effects of inhibition. Nevertheless, there are what seem like simple questions still to be answered. This article presents a brief summary of existing experimental evidence the background and poses questions that remain intriguing for chemists and biochemists researching the chemical enzymology of and drug design for monoamine oxidases (FAD-containing EC 4.1.3.4). Keywords: chemical mechanism; kinetic mechanism; oxidation; protein flexibility; cysteine modifica- tion; reversible/irreversible inhibition; molecular dynamics; simulation 1. Introduction Monoamine oxidase (E.C. 1.4.3.4) enzymes MAO A and MAO B are FAD-containing Citation: Ramsay, R.R.; Albreht, A. proteins located on the outer face of the mitochondrial inner membrane, retained there Questions in the Chemical Enzymology of MAO. Chemistry 2021, by hydrophobic interactions and a transmembrane helix. The redox co-factor (FAD) is 3, 959–978. https://doi.org/10.3390/ covalently attached to a cysteine and buried deep inside the protein [1].