Estrogen Receptor in the Thymus of the Castrated Mice

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Sucrose density gradient ultracentrifugation and dextran-coated charcoal adsorption permitted us to characterize the estrogen-binding proteins in cytosols obtained from the thymus, spleen and mesenteric lymph node of the castrated male and female mice of C57BL strain. The thymic cytosol from both sexes incubated with 3H-estradio1-17β in the presence of excess unlabeled steroids showed a specific estrogen binding 4S protein with its binding capacity of 10-14 moles/mg protein for males and 4×10-15moles/mg protein for females, respectively. The dissociation constant was of 4×10-10M for males and 3×10-10M for females, respectively. No specific binding was, however, found in the cytosols of the spleen and mesenteric lymph node. Steroid analysis by thin-layer chromatography of the thymic cytosols after incubation of them with 3H-estradio1-17β showed that a fair amount (around 60%) of radioactivity was from the undegradated radioactive steroid still bound to4S binder in both sexes. Enzyme study and heat experiment revealed that the estrogen specific 4S binding component in the thymic cytosols bears at least protein in nature and is of heat-labile nature. These results strongly suggest that the thymus of the castrated mice contain a sspecific estrogen receptor, the nature of which is in part protein and heat-labile.
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