Density Lipoproteins

Lipoprotein Density Range (g/mL) Size (nm) Composition (%) Cholesterol Triglycerides Apolipoprotein... 

Lipoprotein Density (g/mL) Protein Phospholipids Free choiesteroi Cholesteryl esters Triacylglycerols... 

Another apolipoprotein, Pa-glycoprotein-1, or apoH, is a glycoprotein of Mr 54,000 found in all major lipoprotein density fractions, especially VLDL where it forms about 4% of the protein mass. Serum concentration is about 15-30 mg/100 ml. Two-thirds to three-quarters is found in the d > 1.21 g/ml fraction after ultracentrifugation (P19, P20). ApoH is taken up readily by a triglyceride-phospholipid emulsion (Intralipid) (P20) and it activates lipoprotein lipase (Nl). Lipoprotein lipase activation by either apoH or apoC-II is inhibited by apoC-III (Nl). 

P9. Patsch, J. R., Sailer, S., Kostner, G., Sandhafer, F., Holasek, A., and Braunsteiner, H., Separation of the main lipoprotein density classes from human plasma by rate-zonal ultracentrifugation. J. Lipid Res. 15, 356-366 (1974). 

Lipoprotein characteristics depends on the varying proportions of protein and lipid present. Lipids are of lower density (<0.9 g/ml) than proteins (>1.28 g/ml), giving a range of lipoprotein densities from 0.9 to 1.21 g/ml. Lipoprotein classification is made according to the respective densities as determined by ultracentrifugation or according to their electrophoretic migration. 

The lipoprotein density that should be employed in Eq. (2) is the buoyant density, which is the density at which the sedimentation coefficient is equal to zero. The buoyant density was obtained experimentally by measuring the sedimentation coefficient at several solvent densities and extrapolating to zero. Kahlon et al. (1982) have shown that the buoyant densities, which they call the a densities, vary with the rotor speed of the centrifuge, reflecting the different compressibilities of water and lipid. In order to convert the lipoprotein density, as determined from its composition, to the buoyant density at a rotor speed of 52,640, the data of Kahlon et al. (1982) were used calculate a correction factor of 0.0016 g/ml, which was added to the compositional densities. The values of buoyant densities listed in Table 11 have been calculated by adding 0.0016 g/ml to the density values determined from their compositions. 

Utilizing the buoyant densities listed in Table II and the frictional ratio of 1.11, values for the sedimentation coefficient have been calculated at two different solvent densities the standard S value routinely used to characterize human serum lipoproteins is defined as value of the flotation coefficient in Svedberg units (the negative sedimentation coefficient X 10 sec) in an aqueous NaCl solvent with a density of 1.063 g/ml and a viscosity of 1.021 centipoise (the viscosity of a 1.063 g/ml sodium chloride solution at 26°C). These values are listed in Table II. The S value is very sensitive to small variations in lipoprotein density because the solvent density is close to the lipoprotein density. To compare the particle sizes or molecular weights, values of the sedimentation coefficient (5) in a solvent with a density of 1.20 g/ml and the viscosity of KBr at 25°C are preferred, and the computed values are listed in Table II. 

A remarkable observation was made by Yao et al. (1991), who expressed a homologous series of C-terminal truncated apoB molecules in stably transfected McArdle 7777 cells, a rat hepatocyte cell line. Plotting the buoyant density of the secreted lipoproteins as a function of the logarithm of the number of amino acid residues, they noticed a linear relationship between these two quantities, implying that the lipoprotein density was inversely proportional to the apoB size. Evidently some fundamental architectural principle was being explored in their studies. 

Plasma lipoproteins Density g ml ) Diameter (nm) Apolipoprotein Physiological role TAG Composition CE C (%) PL P... 

Apolipoprotein Lipoprotein Density Class Approximate Plasma Concentration (mg/dL) Approximate Molecular Weight (kDa) Reported Functions Major Site of Synthesis... 

N3. Niu, X., Zammit, V., Upston, J. M., Dean, R. T., and Stocker, R., Coexistence of oxidized lipids and alpha-tocopherol in all lipoprotein density fractions isolated from advanced human atherosclerotic plaques. Arterioscler. Thromb. Vase. Biol. 19, 1708-1718 (1999). 

Wang CS, Alaupovic P, Gregg RE, Brewer HB Jr (1987) Studies on the mechanism of hypertriglyceridemia in Tangier disease. Determination of plasma lipolytic activities, ki values and apoUpoprotein composition of the major lipoprotein density classes. Biochem Biophys Acta 920 9-19... 

In order to get an answer to the question, what happens in vivo, when LCAT is acting, we incubated whole plasma in the presence of active LCAT, or alternatively LCAT was inhibited by the addition of 5 mAf iodoacetate [6]. After incubation for 24 h at 37°C, several lipoprotein density fractions were separated by ultrazentrifugation (Fig. 2). 

Lipoprotein Density Diameter (g/ml) (nm) Major lipids Major apolipoproteins Protein Triacyl- glycerol Cholesterol Phos- pholipid td O > n... 

Earner, C. D. Henriquez, R. R. Johnson, J. D. MacFarlane, R. D. Developing high performance lipoprotein density profiling for use in clinical studies... 

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