Human low density lipoprotein structure: correlations with serum lipoprotein concentrations.

Human low density lipoproteins (LDL) were isolated and purified from individuals having widely differing serum lipid concentrations. Very low density lipoproteins (VLDL) and high density lipoproteins (HDL) were also isolated and quantitated. HDL2 and HDL3 were separated by flotation velocity in the analytical ultracentrifuge and their relative weight percent determined. The mean density of LDL from 41 individuals was determined by flotation velocity at two different solvent densities. The mean density of LDL was directly proportional to the triglyceride (r = 0.65) and VLDL (r = 0.50) concentrations and inversely proportional to the HDL (r = -0.55) and HDL2 (r = -0.74) concentrations (all significant at P less than 0.001). The mean molecular weight of LDL from 42 individuals was determined by flotation equilibrium centrifugation. The mean molecular weight of LDL was directly proportional to the HDL (r = 0.49) and HDL2 (r = 0.48) concentrations and inversely proportional to the serum triglyceride (r = -0.60) and VLDL (r = -0.48) concentrations (all significant at P less than 0.005 except triglyceride--P less than 0.001). The molecular weight of LDL was inversely proportional to its density, and thus inversely proportional to its protein/lipid ratio which was confirmed by composition measurements. The density and molecular weight of LDL had no relationship to the concentration of LDL (r = 0.04 and 0.03).