Exploration of binding of C.I. Food Red 9 with pepsin by optical spectroscopic and molecular docking methods

A comprehensive study of the effects of C.I. Food Red 9 on the conformation and activity of pepsin was performed using multi-spectral methods and molecular docking technique. Fluorescence and circular dichroism spectral analyzes showed that C.I. Food Red 9 binding induced the changes of secondary and tertiary structure of pepsin. The activity experimental results indicated that the activity of pepsin decreased remarkably with the increasing concentration of C.I. Food Red 9. Multi non-covalent interactions including hydrogen bonds, hydrophobic, and electrostatic forces played important roles in the complex formation between C.I. Food Red 9 and pepsin. The binding constants of pepsin with C.I. Food Red 9 were (1.21   ±   0.036)   ×   10 4   L   mol −1 (298   K) and (1.05   ±   0.043)   ×   10 4   L   mol −1 (310   K). Moreover, the putative binding site of C.I. Food Red 9 on pepsin was near to activity pocket. This study demonstrates that C.I. Food Red 9 could cause some negative effects on pepsin.