Lipoprotein lipids, extractability with ether

Equilibration and exchange suggest that lipids are loosely associated with the low density lipoprotein molecular complex. However, only a part of the lipoprotein lipid can be extracted with ether (Avigan 1957). Ether extractability was enhanced when the lipoprotein was subjected to limited proteolysis with trypsin and chymotrypsin (Banaszak and... 

Kelley (1964) found that proteolysis completely destroyed 20 percent of the lipoprotein molecules in a low density lipoprotein solution. The lipid from these molecules was transferred to the remaining lipoprotein molecules which were less stable during storage but resistant to proteolytic enzyme attack. The additional lipid associated with modified lipoproteins may explain the enhanced ether extractability observed previously. These experiments indicate that lipid-protein interactions contribute to the stability of the molecular complex. 

Detailed studies of the apolipoproteins require the removal of the lipid from the lipoproteins. This can be achieved by extraction of the lipoproteins either direct from plasma or in the precipitated form with ethanol-diethyl ether mixtures (3 1, v/v). The more powerful lipid solvent, chloroform-methanol (2 1, v/v) results in a poorly soluble apolipoprotein. With ethanol-ether, however the advantage of having a soluble apoprotein is partly offset by the loss of 20% of VLDL protein. Lyophilization before... 

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