Effects of Phospholipid and Surface Pressure on Lipoprotein Lipase–Lipolysis of Triglyceride in Monolayers

Abstract

Lipoprotein lipase (LPL)! catalyzed lipolysis of triolein (TO) were investigated in mixed monolayers of TO and egg phosphatidylcholine (PC) or sphingomyelin (SM) at the air/water interface. Binding of LPL to TO/PC mixed monolayers was independent of the surface pressure and lipid composition of monolayer, but LPL did not bind to a pure PC monolayer. This result suggests that the lipid substrate is necessary for the binding of LPL to the interfacial monolayer. The binding amount of LPL to TO/SM mixed monolayer was about 3! fold lower than that to TO/PC mixed monolayer, indicating that SM inhibited the adsorption of LPL. LPL did not hydrolyze TO/PC or TO/SM mixed monolayers at a surface pressure of 8.0 mN/m. However, at a surface pressure of 12.5 mN/m, LPL hydrolyzed the mixed monolayers in a TO content dependent way. Since LPL hydrolyzed condensed monolayers of trimyristin (Arimoto et al, Colloid Polym. Sci., 275, (1997)), these results suggest that the interfacial orientation of TO, not the surface composition, is crucial in the formation of substrate! LPL complexes at the interface and that vertical orientation of acyl chains in the monolayer is favorable for LPL catalyzed! lipolysis.