Preparative isoelectric focusing of human serum very low-density and low-density lipoproteins

Ten percent glycerol prevented the usual precipitation of human serum very low-density lipoproteins (VLDL) and low-density lipoproteins (LDL) at their isoelectric points during their preparative isoelectric focusing (IEF), IEF separated VLDL and LDL into two major fractions. The observed optical density peaks are not artifacts caused by binding of Ampholines to VLDL or LDL since no radioactivity accumulated in the fractions containing VLDL or LDL during IEF in the presence of [ 14C]Ampholine, and gel filtration completely separated the lipoproteins from [ 14C]Ampholine. These results suggest that IEF may separate subspecies of VLDL and LDL under suitable experimental conditions.