Inhibition of tyrosinase by fumaric acid: Integration of inhibition kinetics with computational docking simulations

Fumaric acid (FA), which is naturally found in organisms, is a well known intermediate of the citric acid cycle. We evaluated the effects of FA on tyrosinase activity and structure via enzyme kinetics and computational simulations. FA was found to be a reversible inhibitor of tyrosinase and its induced mechanism was the parabolic non-competitive inhibition type with IC50 = 13.7 +/- 0.25 mM and K-i (slope) = 12.64 +/- 0.75 mM. We newly established the equation for the dissociation constant (K-islope) for the parabolic inhibition type in this study. Kinetic measurements and spectrofluorimetry studies showed that FA induced regional changes in the active site of tyrosinase. One possible binding site for FA was identified under the condition without L-DOPA. The computational docking simulations further revealed that FA can interact with HIS263 and HIS85 at the active site. Furthermore, four important hydrogen bonds were found to be involved with the docking of FA on tyrosinase. Our study provides insight into the mechanism by which dicarboxylic acids such as FA inhibit tyrosinase. By inhibiting tyrosinase and its central role in pigment production, FA is a potential natural antipigmentation agent. (C) 2016 Elsevier B.V. All rights reserved.