THE MACROMOLECULAR COMPOSITION OF HEN'S EGG YOLK AT SUCCESSIVE STAGES OF MATURATION

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Abstract
Yolk at different stages of its formation was separated into its major macromolecular fractions, namely, granules, low-density fraction (LDF), and water-soluble fraction (WSF), and the components of these fractions were examined by ultracentrifugal, electrophoretic, and chromatographic methods. Total yolk solids and the amounts of the several fractions all increased exponentially during yolk formation but at differential rates for different fractions. The proportion of LDF increased rapidly to a maximum (76% of total solids) for yolks weighing 2–5 g, and then declined. Both the WSF and granule fractions decreased in proportion during the early period of yolk formation and then increased slightly as yolk neared maturity. Of the WSF components, the proportions of α-livetin (serum albumin) and β-livetin increased somewhat and γ-livetin (serum γ-globulin) decreased slightly, during yolk maturation. The major granule subfraction, PvLv, showed an increased proportion of phosvitin and α-lipovitellin relative to β-lipovitellin during yolk formation. This increase in the proportions of the phosphorus-rich proteins was not paralleled by a corresponding increase in PvLv phosphorus, which suggests that other phenomena may be involved.