Comparative Studies of the Binding of Six Phthalate Plasticizers to Pepsin by Multispectroscopic Approach and Molecular Modeling

To explore the binding mechanism of phthalate plasticizers with digestive proteases, their effects on conformation and activity of pepsin by multispectroscopic approach and molecular modeling were investigated. Fluorescence spectra combined with UV-vis and circular dichroism (CD) spectra measurements indicated that the six phthalate plasticizers induced the changes of tertiary and secondary structure of pepsin. The solvent polarity of environment around both Trp and Tyr residues on pepsin were affected by phthalate plasticizers. By analyzing the fluorescence quenching and theoretical calculation data, it was concluded that a binding site exists for each phthalate plasticizer in pepsin with different binding ability. The hydrophobic, hydrogen bonding, and Pi-Pi stacking interactions were involved in the interactions between pepsin and phthalate plasticizers. Moreover, the activity assay indicated that phthalate plasticizers were not powerfully inhibitors or activators for pepsin. These studies demonstrated that phthalate plasticizers could cause some negative effects on pepsin. The present studies may provide a way to analyze the biological safety of phthalate plasticizers on digestive proteases or other proteins.