Interaction of lipoprotein lipase with homogeneous lipid emulsions.

The central function of lipoprotein lipase (LpL) is to hydrolyze triacylglycerols in chylomicrons and very low den- sity lipoproteins. We have examined the binding of purified milk lipoprotein lipase to homogeneous synthetic lipid emul- sions, Emulsions composed of either naturally occurring ester- linked lipids or the non-hydrolyzable ether analogues were prepared by sonication and pressure extrusion, and fraction- ated by sucrose density gradient centrifugation. Flotation analysis using the analytical ultracentrifuge indicated that the individual fractions were relatively homogeneous with respect to size with flotation coefficients and molecular weights for the separated fractions ranging from 100 to 1100 S and 5.2 X lo7 to 6.0 X lo8, respectively. Purified milk lipoprotein lipase bound with high affinity and in a saturable manner to emul- sions prepared from the non-hydrolyzable ether-linked lipid analogues of l-oleoyl, 2-palmitoyl phosphatidylcholine and triolein. At low concentrations of LpL, the enzyme caused ag- gregation of the emulsion particles by interparticle cross-link- ing. At higher LpL concentrations, the flotation coefficient of the emulsions decreased significantly with a concomitant increase in particle density. At saturation, the number of LpL monomers bound to lipid particles of radii 67, 75, and 79 nm was 1315, 1449, and 1466, respective1y.I The results demon- strate close packing of LpL on the lipid surface and are consis- tent with there being little disruption to the overall structure