Evidence for Protein Subunits in Low Density Lipoprotein from Pig Serum

Abstract

The two low density lipoproteins (LDL₁ and LDL₂) in pig serum were isolated and their aqueous solutions extracted with ethyl ether. On ultracentrifugation four components of 13, 20, 24 and 30S were evident in both fractions, and occasionally a fifth of 10S could be detected. The 13S component represented about 70% of the extracted material and its protein moiety was estimated to be half that of the parent lipoprotein. This shows that both LDL fractions contain protein subunits that dissociate on lipid extraction, and these apparently reassociate to form the heavier components. Apart from lipid content the only difference between LDL₁ and LDL₂ was a small, but statistically significant, difference in the histidine content.