Vol.:(0123456789) 1 3 The Protein Journal https://doi.org/10.1007/s10930-019-09834-7 The Relevance of Glutathione Reductase Inhibition by Fluoxetine to Human Health and Disease: Insights Derived from a Combined Kinetic and Docking Study Ozlem Dalmizrak 1  · Kerem Teralı 1  · Evelyn Bright Asuquo 1  · Izzet Hamdi Ogus 1  · Nazmi Ozer 1 © Springer Science+Business Media, LLC, part of Springer Nature 2019 Abstract Glutathione reductase (GR) is a homodimeric enzyme playing an important role in the regeneration of the central antioxidant molecule reduced glutathione (GSH) from oxidized glutathione (GSSG) at the expense of a molecule of NADPH. GSH scav- enges and eliminates superoxide and hydroxyl radicals non-enzymatically or serves as an electron donor for several enzymes. Fluoxetine (FLU), a selective serotonin reuptake inhibitor, is widely prescribed in the treatment of major depressive disorder. Here, using enzyme kinetic studies and molecular docking simulations, we aimed at disclosing the mechanistic and structural aspects of the interaction between GR and FLU. Afecting enzyme activity in a dose-dependent manner, FLU was shown to be a moderately potent (IC 50 = 0.88 mM) inhibitor of GR. When the variable substrate was GSSG, the type of inhibition was linear mixed-type competitive (K i = 279 ± 32 μM; α = 5.48 ± 1.29). When the variable substrate was NADPH, however, the type of inhibition was non-competitive (K i = 879 ± 82 μM). The observed diference in inhibition types was attributed to the binding of FLU in the large intermonomer cavity of GR, where it hampered catalysis and interfered with substrate binding. Overall, although it is anticipated that long-term use of FLU leads to acquired GR defciency, the inhibitory action of FLU on GR may be therapeutically exploited in anti-cancer research. Keywords Glutathione reductase · Fluoxetine · Linear mixed-type competitive inhibition · Non-competitive inhibition · Molecular docking Abbreviations FAD Flavin adenine dinucleotide FDA Food and Drug Administration FLU Fluoxetine GPx Glutathione peroxidase GR Glutathione reductase GSH Reduced glutathione GSSG Oxidized glutathione, glutathione disulfde GST Glutathione S-transferase IC 50 Half-maximal inhibitory concentration K i Inhibition constant, dissociation constant of the enzyme‒inhibitor complex K m Michaelis constant K s Dissociation constant of the enzyme‒substrate complex NADP Nicotinamide adenine dinucleotide phosphate, oxidized form NADPH Nicotinamide adenine dinucleotide phosphate, reduced form NFLU Norfuoxetine PLIP Protein‒ligand interaction profler ROS Reactive oxygen species SOD Superoxide dismutase SSRI Selective serotonin reuptake inhibitor TAS Total antioxidant status TPT Transplacental transfer V m Maximum velocity * Nazmi Ozer nazmi.ozer@neu.edu.tr Ozlem Dalmizrak ozlem.dalmizrak@neu.edu.tr Kerem Teralı kerem.terali@neu.edu.tr Evelyn Bright Asuquo 20145086@std.neu.edu.tr Izzet Hamdi Ogus izzethamdi.ogus@neu.edu.tr 1 Department of Medical Biochemistry, Faculty of Medicine, Near East University, Near East Boulevard, Nicosia/TRNC, Mersin 10 99138, Turkey