Selective solubilization of apolipoproteins from hen's egg yolk very low density lipoprotein with guanidine hydrochloride and urea

The selective solubilization of apo-very low density lipoprotein (apo VLDL) of hen's egg yolk was achieved from intact VLDL with guanidine hydrochloride (GuHCl) or urea. The amount of extracted apoVLDL increased with increase of the reagent concentration. GuHCl was more effective than urea and more than 60% of apoVLDL was solubilized with 6 M GuHCl. Previously we reported the presence of five major apoVLDL components, GPI, ApoA, GPII, ApoB, and ApoC in order of size, and found that GPI and GPII were periodic acid-Schiff staining positive, while ApoA, ApoB, and ApoC were negative. With GuHCl or urea, GPI and GPII were easily solubilized, while ApoA and ApoB could not be extracted. The solubilized apoVLDL was rich in carbohydrates, especially sialic acid, compared with the residual apoVLDL. However, only slight differences in amino acid compositon were found between the soluble and the residual apoVLDL. After the partial removal of apoVLDL with GuHCl or urea, VLDL retained its particulate nature, and no destruction of the lipid core was observed. These results were interpreted as indicating that the release of apoVLDL with GuHCl or urea occurred from the surface of the VLDL particle and that the selectively solubilized apoVLDL fractions, such as GPI and GPII, were weakly bound to lipids on the surface of VLDL, while ApoA and ApoB were tightly associated with the VLDL particle.