Effects of Bisphenol S on the Structures and Activities of Trypsin and Pepsin

The effects of bisphenol S on the structures and activities of trypsin and pepsin were investigated by various methods like UV–visible absorbance, fluorescence, circular dichroism, and molecular docking. The secondary and tertiary structures of trypsin and pepsin were altered by bisphenol S binding, which resulted in the loosening of the skeletons of trypsin and pepsin. In addition, bisphenol S induced microenvironmental changes around tyrosine and tryptophan residues of trypsin and pepsin. The activity experimental results showed that the activity of pepsin decreases obviously with the increasing concentration of BPS, while the activity of trypsin does not change remarkably. The binding and thermodynamic parameters obtained by molecular docking and fluorescence spectroscopy showed that the bindings of bisphenol S to trypsin and pepsin were spontaneous processes and hydrogen bonding and hydrophobic interactions played a vital role in stabilizing the bisphenol S–trypsin and bisphenol S–pepsin complexes. The binding constants (KA) of bisphenol S with trypsin were 7.42 × 104 (298 K) and 5.91 × 104 L/mol (310 K), and those of pepsin were 5.78 × 104 (298 K) and 4.44 × 104 L/mol (310 K). Moreover, there was one main kind of binding site for bisphenol S on trypsin or pepsin.