1. Oestrogen treatment induces the formation of a Ca2+-binding glycolipophosphoprotein, vitellogenin, in Xenopus laevis. 2. The incorporation of l-[4,5-3H]-leucine into vitellogenin in vivo and in vitro was observed 12–24h after hormone treatment and increased progressively up to 21 days after treatment. 3. Vitellogenin is shown to be the major protein component biosynthesized and released into the incubation medium in vitro by livers from oestrogen-treated animals. 4. The biosynthesis in vitro of vitellogenin was inhibited by cycloheximide and carbonyl cyanide m-chlorophenylhydrazone, stimulated by increased Ca2+ concentrations and decreased by raising the incubation temperature from 22 to 37°C. 5. Incorporation of labelled amino acids into vitellogenin began after approx. 2h. No lag phase was noted for the incorporation of labelled amino acids into total tissue proteins. 6. The incorporation of label from [32P]phosphate and [2-14C]acetate into the protein as well as into the lipid moiety of vitellogenin showed a lag phase similar to that noted for the incorporation of amino acids. 7. These results suggest that the release of vitellogenin into the incubation medium occurs about 2h after the initiation of its biosynthesis.

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