Determination of physical properties of bovine serum lipoproteins by analytical ultracentrifugation

Abstract

Pure samples of low density lipoprotein-one (d 1.019 to 1.039 g/ml), low density lipoprotein-two (d 1.039 to 1.060 g/ml), and high density lipoprotein (d 1.060 to 1.210 g/ml) were isolated from bovine serum and their properties studied in the analytical ultracentrifuge. Approach-to-equilibrium experiments indicated that the lipoprotein classes were homogeneous. Molecular weights of the lipoproteins given by this method (low density lipoprotein-one, 1.14 x 10(6); low density lipoprotein-two, 2.37 x 10(6); high density lipoprotein, .576 x 10(6)) agreed well with those obtained by a high-speed-equilibrium method (1.03 x 10(6), 2.15 x 10(6), and .567 x 10(6)). Linear plots of flotation rate (corrected for viscosity) against the density of the medium were obtained in sedimentation velocity experiments and on extrapolation gave values for the hydrated density of 1.032 g/ml for low density lipoprotein-one, 1.044 g/ml for low density lipoprotein-two, and 1.071 g/ml for high density lipoprotein. The density of the material which would have to be added to high density lipoprotein to give it the physical properties of low density lipoprotein one was less than 1 g/ml, which suggested that it was predominantly lipid.