Effect of pH on the Interaction of Lutein with Bovine Serum Albumin Studied by Fluorescence Spectroscopy

The interaction between lutein and bovine serum albumin (BSA) was investigated using fluorescence emission spectroscopy under different pH (3.0, 5.0 and 7.4) conditions. The quenching constant and thermodynamic parameters were calculated using a mathematical model. The fluorescence quenching and conformation changes of BSA were analyzed, and the binding sites were determined by site marker competitive experiments and molecular docking. Fluorescence spectra showed that lutein had a fluorescence quenching effect on BSA under different pH conditions. The quenching constant was the highest and the binding constant was larger at pH 7.4 and 298 K. The thermodynamic parameters and molecular docking showed that the binding of lutein with BSA was mainly driven by hydrophobic interaction. Synchronous fluorescence spectra indicated that lutein and the change of pH jointly induced the conformational changes of BSA. The results of site marker competitive experiments and molecular docking showed that the binding site of lutein and BSA was located between subdomains ⅡA and ⅢA, but closer to Sudlow’s site Ⅱ at pH 7.4 and 5.2. At pH 3.0, the binding site was neither near subdomain IIA nor near subdomain ⅢA. Altogether, the results revealed that pH influenced the binding of lutein and BSA, which may provide a theoretical basis for understanding the interaction between proteins and bioactive components.