Comparative studies on the interaction of ascorbic acid with gastric enzyme using multispectroscopic and docking methods

Abstract

Pepsin is the main digestive protease enzyme, is released by the gastric chief cells in the stomach. Ascorbic acid is an essential nutrient that is one of the most prevalent antioxidant nutrients. In this study, experimental and computational methods were used to investigate noncovalent interactions of ascorbic acid and pepsin. UV–vis spectra of results suggested that ascorbic acid–pepsin complexes were formed. The results of fluorescence spectroscopy show that the quenching mechanism was static. Further, the thermodynamic parameters revealed that the binding process of ascorbic acid to pepsin was spontaneous. The negative signs for enthalpy (ΔH°) and entropy (ΔS°) from the interaction of the ascorbic acid–pepsin complex shows that the major driving forces are the van der Waals interactions and hydrogen bond which is agreed with the molecular docking observations.Based on far-CD spectra of pepsin, the α-helix content decreased, followed by an increase in β-sheet compositions. The result of the RMSF value shows that the residues involved in the complex are less flexible. From MD simulation we observed that an average RMSD in complex (1.16 nm) lower than of the free pepsin system(1.44 nm) which agreed with the research of thermal stability (increase in Tm). Kinetic studies showed that by adding ascorbic acid, an increase in enzyme activity happened.