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

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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 Mw = 5.4 X 105 by light-scattering methods, and Mn = 3.4 X 105 by osmotic pressure. A "light" fraction obtained by centrifuging and representing 38% of the soluble material had Mw = 3.4 to 3.5 X 105. Heterogeneity in lipid content appears to be responsible for the low molecular weight (Mw = 2.4 X 105) obtained by sedimentation.