Preliminary investigation on interaction mechanism between nicotine and pepsin
In order to investigate the absorption characteristics of the human stomach to nicotine (NIC) originating from tobacco products for oral use, different concentration levels of nicotine in a citric acid and sodium citrate buffer solution (pH = 2.0) were used to stimulate gastric conditions. After interaction of pepsin with the different levels of nicotine, the 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. Consequently, the action mechanism between nicotine and pepsin was preliminarily studied. The results of spectroscopy and molecular docking simulation indicated that: 1) The quenching mechanism of NIC on pepsin was static fluorescence quenching; 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) The interaction between NIC and pepsin not only increased the polarity of the microenvironment of amino-acid residues in pepsin, but also changed the C=O, C-H and N-H of polypeptide chain of pepsin, which further resulted in the variation of conformation and spatial structure of pepsin; at the same time NIC obviously promoted the activity of pepsin when it was added into pepsin at different concentrations. The results from the study provide references for the development, quality control and health risk evaluation of tobacco products for oral use.