Lipoproteins are composed of a central core in which the more lipophilic components, cholesterol esters and triglycerides, are sequestered from the aqueous environment of plasma by a surface comprised of unesterified (free) cholesterol, phospholipids, and apolipoproteins. These components exist in distinct proportions in the different lipoprotein classes, thereby permitting their separation by operational means such as ultracentrifugation and electrophoresis. There is, however, considerable heterogeneity within each lipoprotein class (Fig. 6.3). Several apolipoproteins are found in the different lipoprotein classes, each having three major functions: structural; as ligands for receptors; and as enzyme cofactors.
