Investigation of the binding mechanism and inhibition of bovine liver catalase by quercetin: Multi-spectroscopic and computational study

The study on the side effects of various drugs and compounds on enzymes is the main issue for monitoring the conformational and functional changes of them. Quercetin (3,5,7,3ʹ,4ʹ-pentahydroxyflavone, QUE), a polyphenolic flavonoid, widely found in fruits, vegetables and it is used as an ingredient in foods and beverages. The interaction of bovine liver catalase (BLC) with QUE has been studied in this research by using different spectroscopic methods. Methods: In this work, the interaction of QUE with BLC was investigated using different spectroscopic methods including ultraviolet-visible (UV-vis) absorption, circular dichroism (CD) and fluorescence spectroscopy and molecular docking studies. Results: Fluorescence data at different temperatures, synchronous fluorescence, and CD studies revealed conformational changes in the BLC structure in the presence of different concentration of QUE. Also, the fluorescence quenching data showed that QUE can form a non-fluorescent complex with BLC and quench its intrinsic emission by a static process. The binding constant (Ka) for the interaction was 104, and the number of binding sites was obtained ~1. The ΔH, ΔS, and ΔG changes were obtained, indicating that hydrophobic interactions play a main role in the complex formation. In vitro kinetic studies revealed that QUE can inhibit BLC activity through noncompetitive manner. Molecular docking study results were in good agreement with experimental data, confirming only one binding site on BLC for QUE at a cavity among the wrapping domain, threating arm and β-barrel. Conclusion: Inhibition of BLC activity upon interaction with QUE demonstrated that in addition to their beneficial effects, they should not be overlooked for their side effects.