Ultracentrifugal and electrophoretic analysis of the water-soluble fraction of chick embryo yolk

Water-soluble proteins, mainly livetins (α-, β-, γ-), are present in hen egg yolk (Martin, Vandegaer & Cook, 1957). They represent 5% of fresh yolk solids (Saito, Martin & Cook, 1965). During the later stages of incubation the watersoluble proteins (water-soluble fraction, WSF) undergo a marked increase in relative proportion; after 15 days of incubation they form over 15% and at 18 days over 40% of yolk-residual solids (Saito et al . 1965). This proportional increase of the WSF is tentatively explained by the passage of egg-white proteins into yolk (Mclndoe, 1960; Saito et al . 1965). Indeed some egg-white proteins (ovalbumin, conalbumin and lysozyme) have been found in the yolk from 14 to 15 days of incubation (Saito & Martin, 1966; Carinci, Wegelin & Manzoli-Guidotti, 1966). At these stages ovalbumin is present in the yolk in such a great quantity that it is difficult to detect qualitative and quantitative changes of other proteins without resorting to further fractionations.