Interfacial binding and activity of lipases at the lipid-water interface: Effects of Gum Arabic and surface pressure

We investigated the effects of Gum Arabic (GA) on the interfacial binding and activity of human pancreatic lipase (HPL) on trioctanoylglycerol (TC8) emulsion. Using the pH-stat technique, in the presence of sodium taurodeoxycholate (NaTDC) at concentration of 0.5 mM or higher, GA had no effect on the HPL activity measured in the presence of colipase. However, in the absence of bile salts or at low bile salt concentration, GA inhibited the HPL activity when TC8 emulsion was used as substrate. At 3% (w/v, final concentration), GA strongly desorbed pure HPL from the TC8 interface and the classical anchoring effect of colipase was clearly observed. An excellent correlation was therefore observed between the interfacial binding and the lipase activity of HPL as measured on a TC8 emulsion. In conclusion, GA was found to be surface active and to have similar effects to those of bile salts on the interfacial binding and activity of HPL. Using the monomolecular film technique, coupled to an ELISA, the penetration of Humicola lanuginosa lipase (HLL) into monomolecular films of non-hydrolysable enantiomeric substrate analogues (1,2-didecanoyl-3-deoxyamino-3-O-methyl glycerol (R3) or 2,3-didecanoyl-3-deoxyamino-1-O-methyl glycerol (S3)) spread at the air-water interface was monitored at constant surface pressure. By combining the surface area variations and the surface excess of HLL, the cross-sectional area of HLL molecule was estimated and a model for its penetration/orientation into the monomolecular films of R3 or S3 was proposed. No significant difference was found in term of HLL molecular area when using these films, indicating that the chirality of the lipid has no significant effect on HLL penetration. Nevertheless, This penetration was found to be deeper at low surface pressures.