Lipoproteins form the most complex blood plasma macromolecules. This attribute of lipoproteins is the main reason that our knowledge of this biological system is still fragmentary in spite of great interest shown and progress made in lipoprotein investigations. Numerous investigations have been reported on composition, structure, metabolism and function of lipoproteins during the last three decades and are summarized in a number of reviews of which three adequately represent these studies (Tria and Scanu, 1969; Nelson, 1972; Scanu and Lands- berger, 1980). The presence of lipids in clear solution in blood plasma of a normal lipemic mammal at the concentration of 200-900 mg/100 ml is made possible by their unique association in water-soluble complex proteins, the lipoproteins. Lipoproteins form a broad spectrum of macromolecules and micells which vary considerably in size, from 6000 % in chylomicrons to an average of 86 a in high density lipoproteins, and molecular weights from billions to 200,000 respectively. The amount and quality of lipids vary in lipoprotein molecules, whereas the protein entity, defined as apolipoprotein, seems to remain qualitatively constant. Depending on the relative proportions of lipid and protein in lipoproteins, from 98%:2% to 3%:97%, their hydrated densities vary from <i 0.92 g/ml in chylomicrons to 1.30 g/ml in very high density lipoproteins, respectively. In short, lipoproteins form very dynamic, complex and heterogenous groups of blood plasma macromolecules with respect to metabolism, composition, size, hydrated density and immunogenicity. The primary physiological functions of lipoproteins have been defined as lipid transport proteins, and the regulation of lipid metabolism. More recent and incomplete reports seem to indicate that lipoproteins may be involved in other physiological processes as regulatory proteins controlling the synthesis and metabolism of certain biological compounds.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 6. Round tables, , 365–374, 1982
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