Isolation and properties of lipoproteins from normal rat serum.

Three major classes of lipoproteins (VLDL, d <1.006; LDL, d 1.006-1.040; HDL, d 1.063-1.21) were isolated by ultracentrifugal flotation from the serum of normal male Sprague-Dawley rats. Their physical, chemical, and immunological properties were analyzed and compared with those of their water-soluble, essentially lipid-free derivatives. Studies were also carried out on the d > 1.21 fractions. Each product was found to have distinct characteristics, and this was also indicated by spectral analyses carried out by the techniques of circular dichroism and UV absorption spectroscopy. The results provided evidence for the mutual role of the protein and lipids in determining the structure, and perhaps the immunological specificity, of serum lipoproteins.