Estrogen Specificity of the Induction of Lipovitellin Synthesis and Evidence for a Specific Estrogen-Binding Component

Using male South African clawed toads, Xenopus laevis, administration of the common estrogens as well as estradiol-17α brought about the synthesis of both total soluble protein and the specific yolk protein, lipovitellin, in liver. This elevation in synthesis was both dose-responsive and estrogen specific; neither hydrocortisone, progesterone, nor testosterone promoted synthesis. The Parke-Davis compound, CN-55, 945–27, a known inhibitor of the binding of estrogen to specific receptor sites in mammalian tissues, inhibited the synthesis of lipovitellin indicating a possible requirement for binding protein in the Xenopus system. In cell-free preparations of liver, 3H-estradiol-17β was bound to a macromolecule fraction which was excluded by columns of Sephadex G-100 or G-200 in buffers of low ionic strength and sedimented at 11–12 S on linear sucrose gradients.