Comparative studies on interactions ofl-ascorbic acid, α-tocopherol, procyanidin B3, β-carotene, and astaxanthin with lysozyme using fluorescence spectroscopy and molecular modeling methods

Abstract

l-Ascorbic acid, α-tocopherol, procyanidin B3, β-carotene, and astaxanthin are five classic dietary antioxidants. In this study, the interaction between them and lysozyme was investigated by fluorescence spectroscopy and molecular modeling methods. The quenching mechanisms of lysozyme by them are all static quenching at lower concentrations of antioxidants, but at higher concentrations, predominantly by the “sphere of action” mechanisms. The binding constants of lysozyme-antioxidants systems are in the following order as: astaxanthin>β-carotene > procyanidin B3 > l-ascorbic acid>α-tocopherol. Thermodynamic analysis reveals that the binding process of α-tocopherol to lysozyme is synergistically driven by enthalpy and entropy. For the other four antioxidants-lysozyme systems, the binding processes are all entropy process. Synchronous fluorescence spectroscopy shows that the five antioxidants may induce microenvironmental changes of lysozyme. Molecular docking results reveal that the five antioxidants bind into the enzyme active site and lysozyme activity is inhibited, in accordance with the results of lysozyme activity experiment. Practical applications Antioxidants are used worldwide as food additives to protect foodstuffs against deterioration caused by oxidation, such as fat rancidity and color changes. Dietary antioxidant is considered to be a safe natural product. However, it may act as an antinutritional factor, in terms of the inhibition of proteases, when ingested in excess. Lysozyme with high natural abundance is an enzyme known for its unique ability to damage bacterial cell walls, thereby providing protection against bacterial infections. When the diverse endogenous and exogenous ligands enter into the human body, ligand–lysozyme conjugation can be observed. Therefore, lysozyme is selected to investigate the binding characteristics of five classic dietary antioxidants, which is critical in order to understand their possible delivery, consequent availability, and relevant health risks.