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

Water-soluble proteins, mainly livetins (a-, /?-, y-), 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 ah 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. We have studied these changes by ultracentrifugal and electrophoretic analysis of the WSF, of its globulin components and of the egg-white proteins separated by the same procedures.