title: Activation-inactivation of hormone binding sites of the oestradiol-17 beta receptor is a multiregulated process.
abstract: The calf uterus oestradiol-17 beta receptor exists in a hormone binding form, which is phosphorylated on tyrosine, and in a non-hormone binding form, which is dephosphorylated. Two enzymes regulate the number of hormone binding sites of the receptor: a kinase which has been purified from cytosol and a phosphatase purified from nuclei. Recent and new findings on the regulation of this activation-inactivation process are reported. In vitro only a fraction (30-60%) of the receptor binding sites are inactivated by the phosphatase. Evidence is given suggesting that this is due to the production during the inactivation process of a powerful inhibitor of the phosphatase. Ca2+-calmodulin stimulates the kinase activity with a parallel increase of phosphorylation on tyrosine and hormone binding sites of the receptor. Nanomolar concentrations of oestradiol-17 beta also stimulate the kinase to activate hormone binding sites. These results suggest that in intact cells inactivation-activation of the oestradiol receptor is a multiregulated process.
mesh_terms: D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology; D002147:Calmodulin / Q000494:pharmacology; D002417:Cattle; D004958:Estradiol / Q000378:metabolism*; D005260:Female; D066298:In Vitro Techniques; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors; D010766:Phosphorylation; D011494:Protein Kinases / Q000032:analysis; D011959:Receptors, Estradiol / Q000378:metabolism*; D011960:Receptors, Estrogen / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism
chemical_list: D002147:Calmodulin; D011959:Receptors, Estradiol; D011960:Receptors, Estrogen; D014443:Tyrosine; D004958:Estradiol; D011494:Protein Kinases; D010744:Phosphoric Monoester Hydrolases; D002118:Calcium