The Plasma Proteins: Volume II

Lipid transport and metabolism are important features of all higher mammalian life forms, particularly man. In man, approximately 1 % by weight of the serum is composed of lipids, amounting to approximately 15-30 gm of lipids present in the total blood compartment. These lipids are principally of five types—unesterified cholesterol, glycerides, cholesteryl esters, phosphatides, and, at relatively low abundance, unesterified fatty acids. However, with the exception of unesterified cholesterol, each of these lipids is a complex mixture containing many different constituent fatty acids. Nearly all of these lipids are present in the blood stream as constituents of lipoproteins. If, by the term lipoprotein we define all known serum lipid-protein structures, we then include within the serum lipoprotein system such extreme examples of lipoproteins as fatty acid-albumin complexes and the largest chylomicra. These molecules range in molecular weight from 70,000 to 1011 and contain by weight approximately 1 % and 99 % lipid, respectively. However, by far the greatest part of the lipoproteins present in serum range from approximately 200,000 to 10,000,000 molecular weight units and contain from 40 % to 95 % lipid, respectively.