INTERACTION OF LIPOPROTEIN-LIPASE WITH HOMOGENEOUS LIPID EMULSIONS

The central function of lipoprotein lipase (LpL) is to hydrolyze triac ylglycerols in chylomicrons and very low density lipoproteins. We have examined the binding of purified milk lipoprotein lipase to homogeneo us synthetic lipid emulsions. Emulsions composed of either naturally o ccurring ester-linked lipids or the non-hydrolyzable ether analogues w ere prepared by sonication and pressure extrusion, and fractionated by sucrose density gradient centrifugation. Flotation analysis using the analytical ultracentrifuge indicated that the individual fractions we re relatively homogeneous with respect to size with flotation coeffici ents and molecular weights for the separated fractions ranging from 10 0 to 1100 S and 5.2 x 10(7) to 6.0 x 10(8), respectively. Purified mil k lipoprotein lipase bound with high affinity and in a saturable manne r to emulsions prepared from the non-hydrolyzable ether-linked lipid a nalogues of 1-oleoyl, 2-palmitoyl phosphatidylcholine and triolein. At low concentrations of LpL, the enzyme caused aggregation of the emuls ion particles by interparticle cross-linking. At higher LpL concentrat ions, the flotation coefficient of the emulsions decreased significant ly 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, respectively. The results demonstrate close packing of LpL on the lipid surface and are consistent with ther e being little disruption to the overall structure of the emulsion par ticle.