A spectroscopic and thermal stability study on the interaction between putrescine and bovine trypsin

The interaction of putrescine with bovine trypsin was investigated using steady state thermal stability, intrinsic fluorescence, UV-vis spectroscopy, far and near- UV circular dichroism and kinetic techniques, as well as molecular docking. The Stern-Volmer quenching constants for the trypsin- putrescine complex were calculated revealing that putrescine interacted with trypsin via the static fluorescence quenching. The enthalpy and entropy change values and the molecular docking technique revealed that hydrogen bonds and van der Waals forces play a major role in the binding process. Upon putrescine conjugation, the V_max value and the k_cat/K_m values of the enzyme was increased. The results of UV absorbance, circular dichroism and fluorescence techniques demonstrated that the micro environmental changes in trypsin were induced by the binding of putrescine, leading to changes in its secondary structure. The thermal stability of trypsin- putrescine complex was enhanced more significantly, as compared to that of the native trypsin. The increased thermal stability of trypsin- putrescine complex might be due to the lower surface hydrophobicity and the higher hydrogen bond formation after putrescine modification, as reflected in the increase of UV absorbance and the quenching of fluorescence spectra. It was concluded that the binding of putrescine changed trypsin structure and function.