title: Interaction of thyroid hormones and cortisol on binding proteins of cytosol and nuclear extract of human leukocytes.
abstract: Competitive properties of thyroid hormone analogues and cortisol for the binding of triiodothyronine and thyroxine, expressed as apparent inhibition constants (Ki), have been measured in nuclear extract and cytosol proteins of human leukocytes by means of electrophoresis in polyacrylamide gradient gel and charcoal-dextran assay. In the cytosol not only thyroid hormones but also cortisol competed for the binding of triiodothyronine and thyroxine as tested by charcoal-dextran assay. By means of electrophoresis two protein fractions binding thyroid hormones were found: protein fraction designed A (m. w. 100,000) and protein fraction B (m. w. 83,000). In protein fraction A the inhibition constant Ki for thyroid hormones are lower than in protein fraction B. In the protein fraction B not only thyroid hormones but also cortisol competed for the binding of triiodothyronine and thyroxine. In the nuclear extract the thyroid hormones were bound in one protein fraction C (m. w. 58,000) only. In this protein fraction only thyroid hormones, but not cortisol, are competitors for the binding of triiodothyronine and thyroxine and in the following descending order: triiodothyronine, thyroxine, tetraiodothyroacetic acid, thyroxamine and D-thyroxine. The competition of cortisol for the binding of thyroid hormones in cytosol protein fraction B in connection with some serum TBG changes in patients after prednisone administration is discussed.
mesh_terms: D002467:Cell Nucleus / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D006854:Hydrocortisone / Q000097:blood*; D007962:Leukocytes / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000097:blood*; D011988:Receptors, Thyroid Hormone; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
chemical_list: D011956:Receptors, Cell Surface; D011988:Receptors, Thyroid Hormone; D014284:Triiodothyronine; D013974:Thyroxine; D006854:Hydrocortisone