Structure of the Plasma Lipoproteins — A Review
The plasma lipoproteins are complexes of lipid and protein which appear as spherical particles when viewed in the electron microscope with negative staining (Forte and Nichols, 1972). There are four major classes of the plasma lipoproteins (Table 1). They are the chylomicrons, the very low-density lipoproteins (VLDL), the low-density lipoproteins (LDL), and the high-density lipoproteins (HDL). The lipid composition of each of these families decreases from the chylomicrons to the HDL and there is a concomitant decrease in the rate of flotation of each lipoprotein class (Table 1). The chylomicrons have an Sf or flotation rate greater than 400, VLDL 20–400, and LDL between 0–20. The HDL do not float at density 1.063. In a recent review, Eisenberg and Levy (1975) have also pointed to the importance of an intermediate density lipoprotein (IDL) which is isolated between the densities of 1.006 and 1.019 and which have an Sf of 12–20. Each lipoprotein class is heterogeneous with respect to their protein and lipid compositions. At present, there is no universally accepted nomenclature of the lipoprotein proteins or apoproteins. In the present review, we have used the A, B, and C system of Alaupovic (1971). In this system, apoA refers to the apoprotein that are primarily, but not exclusively, found in HDL. ApoB is the major apoprotein of LDL, but also comprises about 35% of the protein of VLDL. ApoC represents a group of small proteins originally described in VLDL but which are also present in HDL.
Table 1. Composition and properties of human plasma lipoproteins
>0.4 × 109
5–10 × 106
2.7–4.8 × 106
1.8–3.6 × 105
KeywordsCholesteryl Ester Plasma Lipoprotein Nuclear Magnetic Resonance Study Polar Head Group Fatty Acyl Chain
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