The incorporation of 65Zn into avian eggs

Abstract

The elimination of Zn in the eggs of the domestic hen following the intramuscular injection of a zinc-glycine complex into the hen was studied using Zn65. Appreciable amounts of the isotope appeared in the egg yolk but not in the white and shell fractions. The inconstant very small amounts of (non-radioactive) Zn found in egg white and egg shell by other workers, and in the white by ourselves, were probably due largely or entirely to contamination. After a single intramuscular injection of the isotope into hens the most highly radioactive eggs were those laid 5-10 days after the injection. In the longest series of eggs studied, about 20% of the injected Zn65 was eliminated in the egg yolks in 37 days, and eggs laid at the end of this period still contained appreciable amounts of Zn65. The Zn65 in the egg yolks was associated with the lipovitellin, and was attached to the protein component (vitellin) of this complex; none was present in the livetin, phosvitin or yolk lipid fractions. The Zn65 present in the lipovitellin was firmly bound. It did not undergo exchange in vitro at pH 714 with the zinc-glycine, and very little of it could be removed by dialysis for 72 hrs. The Zn65 content of any one sample of lipovitellin remained constant, in relation to the nitrogen and phosphorus contents, when the lipoprotein was reprecipitated twice. The possible significance of the Zn in egg yolk is briefly discussed.