Structure of human serum lipoproteins inferred from compositional analysis.

Abstract

COMPOSITIONAL ANALYSIS The basic compositional data used in our analysis were taken from a recent critical compilation by Scanu and Kruski (6). The reported data are based on dry weight and thus they do not take into consideration the possible presence of water in the lipoprotein particle. In our analysis we also assumed the absence of significant amounts of structural water inside lipoproteins. Minor components, such as free fatty acid, carbohydrates, vitamins, and unidentified compounds, were ignored because, at best, they amount to not more than 5% of the total weight (6) and are likely not to play an essential structural role. For very low density lipoprotein (VLDL) and chylomicrons Scanu and Kruski presented only average compositional data. VLDL and chylomicrons are, in fact, particles of rather broad size distribution, and several authors reported compositional data on their subfractions (2, 7). These additional data on subfractions were also used wherever appropriate. Table 1 summarizes the weight percentage compositions of the major constituents of all lipoprotein classes.From the molecular weight and the weight percentage composition, assuming no structural water, one can calculate the number of molecules of each component in a lipoprotein particle ( Table 2). The following molecular weights were used for the calculations: triglycerides, 850; phospholipid, 775; cholesterol ester, 650; and cholesterol, 387. For the protein content it was not useful to calculate the number of protein molecules per particle because the various lipoprotein classes contain a variety of apoproteins of different molecular weights. For comparison it was more suitable to calculate the number of amino acid residues per particle, assuming an average residue weight of 100. Assuming that all lipoproteins are spherical particles, one can calculate from the molecular weight and the density of the particle the radius of an equivalent sphere r in units of A, also shown in Table 2. Since for the average VLDL and chylomicrons no reliable molecular 'weight data were available, we calculated the molecular weight from the experimentally determined average particle radii, 200 A and 600 A, respectively. Triglyceride and cholesterol ester compositionThe major components of lipoproteins can be divided into nonpolar lipids (triglycerides and cholesterol esters) and polar constituents (phospholipids, cholesterol, and protein). If hydrophobic interactions play an important part in organizing the components, then one would expect the existence of a hydrophobic phase, as it has already been suggested for VLDL and 837

Specific sorbent of apolipoprotein B-containing lipoproteins for plasmapheresis. Characterization and experimental use in hypercholesterolemic rabbits.

“…The area of the lipoprotein monomolecular layer was calculated using the factors of 1.9 mg cholesterol/m 2 for VLDL, 3.7 mg/m 2 for LDL, and 1.2 mg/m 2 for HDL. 17 The K values (inverse of affinity) were similar for LDL and HDL, while VLDL had a much higher affinity to the sorbent. The capacity of the sorbent, however, was much smaller for HDL than for VLDL or LDL.…”

“…The molarity of the lipoprotein was calculated using the factors of 1 g of cholesterol/liter = 3.62 x 10" 7 M for VLDL; 1.45 x 10-6 M for LDL; and 2.80 x 10" 5 M for HDL 17 The linear plot of the data according to this equation is shown in Figure 3. The data for each lipoprotein subclass fit to a straight line, which indicates that binding of lipoprotein to the sorbent is, indeed, a simple Langmuir-type adsorptive binding.…”

Remodeling and Shuttling

“…11 The remodeling of HDL by LUVs results in particles that exhibit a greater efficiency and a larger capacity to extract cellular cholesterol. Ordinarily, HDL particles contain relatively few PL molecules (about 50), 43 and incoming UC molecules must compete with apolipoprotein molecules for interaction with these PLs. 44 PL enrichment by LUVs substantially increases the number of PL molecules per particle, which results in an enhancement in the initial rate of sterol removal and in the total capacity of remodeled particles.…”

“…* Estimation of particle size from the partial specific volumes of the constituents according to the method of Shen et al 43 Briefly, the HDL PL and protein contents in original and remodeled particles as described in Table 2 were used to estimate the particle diameters.…”

Lipoprotein changes in children after liver transplantation: Mild hypertriglyceridemia and a decrease in HDL/HDL ratio

“…HDL 2 particles are larger than HDL 3 particles with less surface (apoproteins, phospholipid, free cholesterol) relative to core constituents (cholesteryl ester and triglyceride). 41 Two major pathways, operative in plasma, are responsible for HDL subclass inter- conversions in plasma, a pathway of cholesteryl ester enrichment of HDL, via HDL precursor particles to HDL 3 and then HDL 2 , and concomitantly a pathway of removal of cholesteryl ester through cholesteryl ester/triglyceride exchange between HDL and LDL, followed by hydrolysis of HDL triglycerides. 42 In the presence of hypertriglyceridemia, the neutral lipid transfer processes would be expected to shift the equilibrium toward the smaller HDL 3 particles.…”