Partial specific volume and preferential hydration of low density lipoprotein subfractions

We have determined the partial specific volume ( v ¯ ) for five low density lipoprotein (LDL) subfractions (n=5–7) and evaluated preferential hydration (n=2) for LDL subfraction 3 in normolipoproteinemic subjects in order to characterize these highly atherogenic components of the human plasma lipoprotein spectra. Values for v ¯ at 1 g were determined by sixth place density measurements of the solvent and lipoprotein solutions and carbon, hydrogen and nitrogen (CHN) absolute mass of the lipoprotein concentrations. Mean values for v ¯ were 0.9757±0.0019, 0.9701±0.0007, 0.9674±0.0016, 0.9616±0.0016 and 0.9550±0.0025 ml/g for subfractions 1, 2, 3, 4 and 5, respectively. However, molecular densities (σ) obtained from ϱ(rho)=1/ v ¯ for respective LDL subfractions were 1.0249, 1.0308, 1.0337, 1.0399 and 1.0471 g/ml, respectively. The preferential hydration of lipoprotein subfraction 3 (n=2) in NaCl/H 2 O solutions was 2.9–4.8 wt percent, whereas values were much lower (0.3–0.6 wt percent) in NaCl/NaBr/H 2 O solvent system. Unhydrated densities for LDL subfraction 3 (n=2) at 1 g (sixth‐place density meter) were 1.0287 and 1.0269 g/ml, whereas at 200,000 × g (used in D 2 O flotation ηF o vs ϱ determinations) both values were 1.0308 g/ml, indicating that these similar LDL fractions have 23 and 53% higher compressibility than the solvent at 200,000 × g force. It was observed that the linearity of ηF o vs ϱ may not be valid for solvents NaCl/NaBr/H 2 O of density as high as 1.4744 g/ml. Thus, flotation velocity data using extreme salt concentrations (1.4744 g/ml and higher) may be viewed with caution.