High-density lipoproteins diameters

Fig. 2. Negative-staining electron micrographs of human plasma lipoproteins (diameters 10-1(KX) nm). The laigest particles [chylomicrons (Chylo) and VLDLs] contain a higher ratio of lipid to protein, and are therefore less dense, than low-density lipoproteins (LDLs) and high-density lipoproteins (HDLs) that contain relatively more protein. Photograph courtesy of Dr. R. Hamilton, University of California at San Francisco, with permission.

A specific type of interaction between lipids and proteins is found in lipoproteins which transport triglycerides and cholesteryl esters in the plasma of mammalians. The largest lipoproteins, chylomicrons with a diameter between 800 A and 5000 A, and very-low-density lipoproteins (VLDL), with a diameter of 300-800 A, resemble emulsion droplets with a core of non-polar lipid and a surface coat of phospholipids and proteins (cf. Brown et ai, 1981). A physical characterization of chylomicrons has been reported (Parks et al.y 1981). Most of the plasma cholesterol occurs in low-density lipoprotein (LDL) which is a particle with a diameter of 200 A. The core consists of almost pure cholesteryl esters and a surface coat of a phospholipid monolayer and four tetrahedrally arranged apoproteins (Gulik-Krzywicki et aly 1979). The smallest particle, high-density lipoprotein (HDL), is a kind of molecular lipid-protein complex. 

Determined from the calibration of the column obtained for the standard samples of known particle diameter (24). C chylomicrons, VLDL very low density lipoproteins, LDL low. density lipoproteins, HDL high density lipoproteins, HDLsub HDL subfractions. 

Due to dynamic remodeling within different HDL subfractions and between HDL and other lipoproteins, HDL is a heterogeneous class of lipoproteins that can be generalized by a high density (>1.063 g/mL) and a small size (5- to 17-nm diameter). Differences are characterized by shape, density, size, charge, and antigenicity,... 

The classification into chylomicrons (CM), very low density (VLDL), low density (LDL), and high density (HDL) lipoproteins is based on their relative contents of protein and lipid that determine the densities of these lipoprotein classes. CM have only 1-2% protein while HDL have about 50% protein by weight. The diameters of lipoproteins are inversely correlated with their densities and range from about 6000 A for CM to 70 A for the smallest HDL (Fig. 1). 

Yolk droplets of highly variable size, with a diameter range of 20-40 pm. They resemble fat droplets, consist mostly of lipids, and some have protein membranes. They are a mixture of lipoproteins with a low density (LDL, cf. 3.5.1.2). 

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