Lipoprotein of the density 1.006-1.020 in the plasma of patients with type III hyperlipoproteinaemia in the postabsorptive state.

Using a rate zonal ultracentrifugal technique in 10 patients with type III hyperlipoproteinaemia, very low density lipoproteins (VLDL) (d less than 1.006, S(f) greater than 20), an intermediate lipoprotein density class with a S(f) range of 15 - 20 (Lp III), and low density lipoproteins (LDL) (S(f) 6 - 8) could be isolated from the plasma. The Lp III was found as a symmetrical peak between VLDL and LDL; its plasma concentration was 248 mg/100 ml plasma (mean), 92 - 469 mg/100 ml plasma (range); the Lp III/LDL ratio was 0.65 (mean), 0.25 - 2.3 (range); the chemical composition w/w was 35.8 percent total cholesterol, 19.3 percent triglycerides, 24.3 percent phospholipids, and 20.4 percent protein (mean). In agarose gel electrophoresis, the Lp III migrated faster than LDL, but slower than VLDL. By means of a double immunodiffusion technique and immunoelectrophoresis, apo-Lp B and apo-Lp C were detectable. In an angle head rotor at 1.4 x 10-8 g. min. Lp III can be separated from VLDL at a solvent density of 1.006, and from LDL at a density of 1.025. In the postabsorptive state in one patient with type I hyperlipoproteinaemia, five with type II and 20 with type IV, and in 50 healthy persons of both sexes, this Lp III peak was not found. The finding of a high concentration of Lp III and a rather low concentration of LDL in the plasma of patients with type III hyperlipoproteinaemia can be regarded as further evidence for an impaired catabolism of VLDL to LDL at Lp III ("intermediate" lipoprotein).