MOLECULAR WEIGHT AND PHYSICAL PROPERTIES OF A LIPOPROTEIN FROM THE FLOATING FRACTION OF EGG YOLK

Abstract

Ether extraction removes 80% of the floating fraction of egg yolk from its solution in 2.5% sodium chloride. On removal of the ether and dialysis against specific solvents two thirds of the remaining lipoprotein (40% lipid) precipitates, leaving a soluble fraction containing 50% lipid. The soluble and insoluble portions probably represent different levels of degradation rather than different lipoproteins since both materials are apparently derived by ether extraction from a natural entity of much higher lipid content. The soluble fraction is heterogeneous and has mean molecular weights of M w = 5.4 × 105by light-scattering methods, and M n = 3.4 × 105by osmotic pressure. A "light" fraction obtained by centrifuging and representing 38% of the soluble material had M w = 3.4 to 3.5 × 105. Heterogeneity in lipid content appears to be responsible for the low molecular weight (M w = 2.4 × 105) obtained by sedimentation.