Interaction of lipoprotein lipase with native and modified heparin-like polysaccharides

Abstract

Lipoprotein lipase (EC 3.1.1.34) [from bovine milk], which was previously shown to bind to immobilized heparin, was found to bind also to heparan sulfate and dermatan sulfate and to some extent to chondroitin sulfate. The relative binding affinities were compared by determining the concentration of NaCl required to release the enzyme from polysaccharide-substituted Sepharose, the concentration of free polysaccharides required to displace the enzyme from immobilized polysaccharides and the total amounts of enzyme bound after saturation of immobilized polysaccharides. By each of these criteria heparin bound the enzyme most efficiently, followed by heparan sulfate and dermatan sulfate, which were more efficient than chondroitin sulfate. Heparin fractions with high and low affinity for antithrombin, respectively, did not differ with regard to affinity for lipoprotein lipase. Partially N-desulfated heparin (40-50% of N-unsubstituted glucosamine residues) was unable to displace lipoprotein lipase from immobilized heparin. This ability was restored by re-N-sulfation or by N-acetylation; the N-acetylated product was essentially devoid of anticoagulant activity. Partial depolymerization of heparin led to a decrease in ability to displace lipoprotein lipase from heparin-Sepharose; even fragments of less than decasaccharide size showed definite enzyme-releasing activity. Studies with hepatic lipase (purified from rat post-heparin plasma) gave results similar to those obtained with milk lipoprotein lipase. The interaction between the hepatic lipase and the glycosaminoglycans was weaker and was abolished at lower NaCl concentrations. The ability of the polysaccharides to release lipoprotein lipase to the circulating blood after i.v. injection into rats essentialy conformed to their affinity for the enzyme as evaluated by the experiments in vitro.