Lipoprotein Catabolism

Abstract

The study of lipoprotein degradation poses certain very special problems. The lipoprotein molecule is something of a chimera. Unlike a well-behaved, covalently constructed molecule like DNA or a simple protein, it represents a less tightly bound complex of proteins and lipids — and they don’t sit still. The ready exchange of free cholesterol between lipoprotein molecules is well recognized. The same is true for phospholipids. Thus, it is very difficult to interpret turnover studies based on labeling of these lipid components. As we shall discuss, at least some of the protein moieties also exchange rapidly between lipoprotein fractions. So the investigator is plagued by the vagaries of a system that has maddening, will-o’-the-wisp qualities about it. At least the cholesterol esters, some of the apoproteins, and the triglycerides exchange slowly enough so that kinetic studies can be meaningful and the studies I will review today deal primarily with the latter two moieties.