Abstract
The central function of lipoprotein lipase (LpL) is to hydrolyze triacylglycerols in chylomicrons and very low density lipoproteins. We have examined the binding of purified milk lipoprotein lipase to homogeneous synthetic lipid emulsions. Emulsions composed of either naturally occurring ester-linked lipids or the non-hydrolyzable ether analogues were prepared by sonication and pressure extrusion, and fractionated 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 10(7) to 6.0 x 10(8), respectively. Purified milk lipoprotein lipase bound with high affinity and in a saturable manner to emulsions prepared from the non-hydrolyzable ether-linked lipid analogues of 1-oleoyl, 2-palmitoyl phosphatidylcholine and triolein. At low concentrations of LpL, the enzyme caused aggregation of the emulsion particles by interparticle cross-linking. 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, respectively. The results demonstrate close packing of LpL on the lipid surface and are consistent with there being little disruption to the overall structure of the emulsion particle.
Highlights
The central function of lipoprotein lipase (LpL) is to hydrolyze triacylglycerolsin chylomicronsand very low density lipoproteins
Lipoprotein lipase (LpL) hydrolyzes triacylglycerol (TG), phosphatidylcholine (PC), and diacylglycerol in TGrich very low density lipoprotein particles (VLDL) and chylomicrons.These particles consist predominantly of a TG and cholesteryl ester core surrounded by a monolayer of phospholipids, protein, and unesterified cholesterol [2]
Using emulsions the size of either low density lipoprotein (LDL) or chylomicrons, Tajima, Yokoyama, and Yamamoto [16] showed that the kinetics of triacylglycerol hydrolysis were similar with respect to K, but that Vmxwas greater for the chylomicron-sized particles
Summary
The central function of lipoprotein lipase (LpL) is to hydrolyze triacylglycerolsin chylomicronsand very low density lipoproteins. We have examined the binding of purified milk lipoprotein lipase to homogeneous synthetic lipid emulsions,Emulsions composed of either naturallyoccurring esterlinked lipids or the non-hydrolyzable ether analogues were prepared by sonication and pressure extrusion, and fractionated by sucrose density gradient centrifugation. Purified milk lipoprotein lipase bound with high affinity and in a saturable manner to emulsions prepared from the non-hydrolyzable ether-linked lipid analogues of l-oleoyl, 2-palmitoyl phosphatidylcholine and triolein.At low concentrationsof LpL, the enzyme caused aggregation of the emulsion particles by interparticle cross-linking. The suspension was sonicated at maxispect to size and composition [18, 19] Such studies mum power (amplitude 165 microns) in an MSE highlight the need for a model system consisting of well- Soniprep sonicator (5 X 1 min with 30 s intervals for characterized emulsion particles of homogeneous size cooling) under a constant stream of nitrogen.
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