SEPARATION AND CHARACTERIZATION OF LIPOVITELLIN FROM HEN EGG YOLK

Abstract

The major sedimenting fraction of egg yolk, which appears to be homogeneous in sodium chloride solutions, has been fractionated into lipovitellin, phosvitin, and γ-livetin. By dissolving egg yolk in 0.4 M magnesium sulphate and diluting to 0.2 M much of the phosvitin is precipitated and further dilution of the supernatant yields lipovitellin, from which most of the γ-livetin and contaminating phosvitin can be removed by further treatment. Separation and recovery of both lipovitellin and phosvitin by this procedure indicate that phosvitin is a separate protein and not an integral part of the lipovitellin molecule. When the sedimenting fraction in egg yolk is dissolved in buffer solutions at pH 9.0, γ-livetin can be resolved ultracentrifugally from the rest of this fraction, but precipitation by dilution, with ammonium sulphate, or with ethanol, failed to separate the components. Evidently lipovitellin as prepared in the past by similar methods has been a mixture of three proteins. Lipovitellin containing about 10% γ-livetin and 20% lipid had a molecular weight of 3.2 × 105and a phosphorus content of 0.49%, about half that previously reported.