Effects of proanthocyanidins on porcine pancreatic lipase: Conformation, activity, kinetics and thermodynamics

• The inhibitory rate plateaus at about [PC]/[PL] = 200.
• PC concentration-dependently changes the secondary structure of PL.
• PC quenches the fluorescence of PL both dynamically and statically.
• PC induces aggregation of PL and therefore stabilizes the enzyme.
• PC noncompatitively inhibits the activity of PL.

The interactions between proanthocyanidins (PC) and porcine pancreatic lipase (PL) were investigated from variant aspects of lipase conformation, activity, kinetics, and thermodynamics. Results show that 34% inhibitory rate of PC on PL is achieved after about 30-min incubation, and the inhibitory rate increases with the increase of PC concentration and then plateaus at the PC/PL ratio of 200. Circular dichroism and fluorescence spectroscopic analyses demonstrate that PC decreases the α-helix content while increases the β-sheet content of PL, but does not change the microenvironment of Trp, and PC quenches the fluorescence of PL both dynamically and statically through the formation of PL–PC complex. PC induces PL aggregation and then stabilizes the lipase aggregates. Kinetic studies reveal that PC does not change the Km value while decreases the Vmax value, implying that PC non-competitively inhibits the PL activity.