Preliminary investigation on interaction mechanism between nicotine and pepsin

In order to investigate absorption characteristics of human stomach to nicotine (NIC) in tobacco products for oral use, certain concentration of citric acid and sodium citrate buffer solution (pH = 2.0) were prepared for simulating gastric conditions and different levels of nicotine solutions were prepared by using buffer solution. After interaction of pepsin with different levels of nicotine, spectrum changes of the pepsin before and after addition of different levels of nicotine were observed by various spectroscopic methods i.e. fluorescence spectrum, ultraviolet spectrum, infrared spectrum, circular dichroism spectrum and molecular docking simulation technology. Action mechanism between nicotine and pepsin was studied. Research of spectroscopy and molecular docking simulation indicated that: 1) the quenching mechanism of NIC on pepsin was static fluorescence; 2) NIC and pepsin interacted spontaneously via hydrogen bonding and van der Waals forces; 3) there existed a single high-affinity binding site between NIC and pepsin; 4) interaction between NIC and pepsin increased polarity of microenvironment of amino-acid residues in pepsin, and changed C=O, C-H and N-H of polypeptide chain of pepsin, resulting variation of conformation and spatial structure of pepsin. In the mean time, NIC promoted activity of pepsin when it was added into pepsin at different concentrations. Results of this research can provide references for development, quality control and health risk evaluation of tobacco products for oral use