Lipoprotein-Polyanion-Metal Interactions

Abstract

This chapter discusses lipoprotein–polyanion–metal interactions. Virtually all the plasma lipids are combined with specific proteins in the form of lipoproteins. In the presence of divalent cations, sulfated polysaccharides and sodium phosphotungstate can precipitate at neutral pH all the lipoprotein classes, namely, chylomicrons, very low-density lipoproteins (VLDL), low density lipoproteins (LDL), and high-density lipoproteins (HDL). This precipitation is dependent on the nature of the anion and cation, the concentration of reagents, and the ionic strength. The formation of an insoluble complex is more easily achieved with chylomicrons and VLDL than with LDL, and in turn more easily with LDL than with HDL. This is related to the protein:lipid ratio and not to the composition of the lipid moiety of the individual lipoproteins. Under certain conditions, the precipitation of LDL is complete and selective. By varying the ionic strength, differential precipitation of chylomicrons, VLDL, and LDL, followed by turbidimetric estimation of these lipoproteins, can be accomplished. Serum lipoproteins are also precipitated by divalent cations and polyphosphates, tetracyclines, or anionic detergents.