Spectroscopic analysis on the interaction of ferulic acid and tetramethylpyrazine with trypsin

The interaction of trypsin with tetramethylpyrazine (TMP) and ferulic acid (FA) was studied using fluorescence, synchronous fluorescence, UV-vis absorption, circular dichroism (CD) and three-dimensional (3D) fluorescence spectra techniques. Using fluorescence quenching calculations, the bimolecular quenching constant (kq), apparent quenching constant (KSV), effective binding constant (Ka) and binding site number (n) were obtained. The distance r between donor and acceptor was found to be 2.049 and 1.281 nm for TMP-trypsin and FA-trypsin complexes. TMP and FA can quench the fluorescence intensity of trypsin by a static quenching procedure. Thermodynamic parameters calculated on the basis of different temperatures revealed that the binding of trypsin to TMP/FA mainly depended on van der Waals' forces and hydrogen bonds. The effect of TMP and FA on the conformation of trypsin was analyzed using synchronous fluorescence, CD, 3D fluorescence spectra and molecular docking studies.