Isolation and partial characterization of high-density lipoprotein HDL1 from rat plasma by gradient centrifugation

Abstract

The lipoproteins isolated from rat plasma by flotation in the density range 1.019-1.063 g/ml were further characterized. Using rate zonal ultracentrifugation, 2 lipoproteins were isolated in almost equal proportions from this density range. Similar isolations may be accomplished with density gradients in a swinging-bucket rotor. On isopycnic-density-gradient ultracentrifugation one component banded at .rho. [density] = 1.031 g/ml and the other at .rho. = 1.054 g/ml. More than 98% of the apoprotein of the lighter component was B protein, and hence this particle is LD (low-density) lipoprotein. Of the apoproteins of the .rho. = 1.054 g/ml particles, designated lipoprotein HDL1, over 60% was arginine-rich peptide, and the remainder was A-I, A-IV and C peptides. The MW of these lipoproteins determined by agarose column chromatography was 2.36 .times. 106 for LD lipoprotein and 1.30 .times. 106 for lipoprotein HDL1. On EM the radius of LD lipoprotein was 14.0 nm and that of lipoprotein HDL1 was 10.0 nm, in contrast with molecular radii of 10.4 nm and 8.4 nm, respectively, determined from the gel-permeation-chromatography data. The lipid and phospholipid composition of both particles was determined. Lipoprotein HDL1 was notable for the concentration of its esterified cholesterol, which was similar to that of LD lipoprotein, and the low triacylglycerol content, resembling that of HD lipoprotein. The possible origin of lipoprotein HDL1 is discussed.