Interaction of gallic acid with trypsin analyzed by spectroscopy

The interactions between trypsin and gallic acid (GA) were investigated by means of fluorescence spectroscopy, UV-vis absorption spectroscopy, resonance light scattering (RLS) spectroscopy, synchronous fluorescence spectroscopy, and enzymatic inhibition assay. It was found that GA can cause the fluorescence quenching of trypsin during the process of formation of GA-trypsin complex, resulting in inhibition of trypsin activity (IC₅₀ = 3.9 × 10⁻⁶ mol/L). The fluorescence spectroscopic data showed that the quenching efficiency can reach about 80%. The binding constants were 1.9371 × 10⁴ L/mol, 1.8192 × 10⁴ L/mol, and 1.7465 × 10⁴ L/mol at three temperatures, respectively. The thermodynamic parameters revealed that hydrogen bonds, van der Waals, hydrophobic, and electrostatic interactions were involved in the binding process of GA to trypsin. Molecular modeling studies illustrated a specific display of binding information and explained most of the experiment phenomena. The microenvironments of tryptophan and tyrosine residue in trypsin were changed by the GA. Results indicated that GA was a strong quencher and inhibitor of trypsin.