The effect of triterpenoid saponins on pancreatic lipase in vitro : Activity, conformation, kinetics, thermodynamics and morphology

The molecular interactions between pancreatic lipase (PL) and five triterpenoid saponins compounds, including tea saponin, oleanolic acid, betulin, ginsenoside Ro, and ginsenoside Rd, were investigated in vitro through comprehensive evaluation of PL activity, conformation, reaction kinetics, thermodynamics, aggregation morphology and solubility. All tested saponins inhibited PL activity, and their inhibitory ratios showed structure- and concentration-dependence. Tea saponin possessed competitive inhibition against PL activity, and affected PL secondary structure, while other four saponins non-competitively inhibited PL activity and affected PL tertiary structure. However, all tested saponins could statically quench PL fluorescence. Soluble PL-saponins complexes were characterized by AMF, DLS and Bio-Rad method, and PL showed self-assembly phenomenon in the presence of saponins, which possessed a close contribution to the inhibitory ratios. DSC measurement revealed that five tested saponins compounds had variant influence on PL enzyme thermal stability parameters (Tm and ΔH).