The rat arginine-rich apoprotein and its redistribution following injection of iodinated lipoproteins into normal and hypercholesterolemic rats

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Normal rat plasma was fractionated into very low density (VLDL), low density (LDL), and high density (HDL) lipoproteins by a combination of ultracentrifugation and Geon-Pevikon block electrophoresis. In addition, a previously uncharacterized lipoprotein, referred to as HDL 1, was separated from the LDL in the 1.02-1.063 density fraction. HDL 1 had α 2 mobility by electrophoresis, were cholesterol rich and contained the arginine-rich apoprotein (ARP) as its major protein component. Following cholesterol feeding, there was a marked increase in concentration of the lower density and α 2-migrating lipoproteins (the α 2-migrating lipoproteins are referred to as HDL c in hypercholesterolemic rats), presumably the HDL c represent an increase in the HDL 1 of normal rats. Associated with the various cholesterol-induced lipoproteins including HCL c there was the prominence of the arginine-rich apoprotein. The ARP was isolated from various lipoproteins of normal and hypercholesterolemic rats by gel filtration, DEAE chromatography, and elution from sodium dodecyl sulfate polyacrylamide gels. The identity of the arginine-rich apoprotein in the various lipoproteins was established by amino acid analysis, co-electrophoresis, and immunochemistry. On DEAE chromatography and Tris-urea gel electrophoresis the ARP exhibited heterogeneity which was shown to be due in part to differences in sialic acid content of the various DEAE fractions. Following the injection of [ 1251]-lipoproteins, it was possible to identify and determine the activity associated with the ARP in the VLDL, d = 1.006−1.02, LDL, HDL 1(c), and HDL by SDS gel electrophoresis. The redistribution of the ARP among the various lipoprotein classes was then determined in both normal and hypercholesterolemic rats 2 h after the injection of 125I-labeled VLDL, HDL 1, HDL c, and HDL. In normal rats, the ARP associated with the injected lipoproteins was redistributed primarily to the HDL or was retained by the HDL. However, in the hypercholesterolemic rats, a large portion of the ARP was redistributed to the cholesterol-rich lower density lipoproteins (B-VLDL, 1.006-1.02, LDL and HDL c). The propensity for an association between the cholesterol-induced lipoproteins and the ARP was shown.