Protein Components of Very Low Density Lipoproteins from Hen's Egg Yolk

Abstract

Egg yolk lipoproteins of very low density contain proteins with cofactor activity for lipoprotein lipase. When delipidated, very low density lipoproteins were dissolved in 10 mM HCl and fractionated by gel filtration, about 2/3 of the protein were in several components with estimated MW of 60,000 to more than 170,000. The major low-MW proteins were the dimeric and monomeric forms of a previously characterized 9000-dalton peptide. The cofactor activity was not associated with any of these major proteins. A large-scale fractionation method was developed by which 3 protein fractions with cofactor activity for lipoprotein lipase were purified more than thousand-fold. One fraction had a molecular size of about 9000 daltons and the other had a size of about 5000 daltons. Both these fractions were further separated on the basis of charge into several fractions with cofactor activity. The cofactor proteins were relatively soluble both at high and at low pH. They retained their cofactor activity after denaturation in guanidinium hydrochloride and after reduction. During the initial steps in the purification of the cofactor proteins, another low MW protein followed the cofactors. It had a single 17,500-dalton peptide chain and was present in 4 variants, 3 of which contained carbohydrate.