title: Characterization of the 3,3',5-triiodo-L-thyronine-binding site on plasma membranes from human placenta.
abstract: The binding of [125I]T3 to sites on human placenta plasma membranes was characterized, and the binding site was solubilized after affinity labeling with N-bromoacetyl-[125I]T3 (BrAc[125I]T3). Two classes of T3-binding sites were detected. One class has a high affinity (Kd = 2.0nM) and a low capacity (approximately 320 fmol/mg protein); the other has a low affinity (Kd = 18.5 microM) and a high capacity (approximately 2.2 pmol/mg protein). The binding sites were found to be specific for T3 in that other thyroid hormone analogs (D-T3, rT3, D-T4, and L-T4) were less effective or ineffective in displacing the bound [125I]T3. The affinity labeling ligand BrAc[125I]T3 was found to specifically label a protein with an apparent mol wt of 65,000, as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The BrAc[125I]T3-labeled protein was solubilized with 2 mM 3-[( 3-cholamidopropyl)dimethylammonio]1-propane sulfonate. The apparent mol wt of the labeled protein was between 140,000 and 150,000 by Sephadex-G-200 gel filtration. These data demonstrate that a high affinity binding site specific for T3 is present on plasma membranes from human placenta and that the binding site is a protein, most likely a dimer, with a native mol wt between 140,000 and 150,000.
authors.forename: R
authors.initials: R
authors.lastname: Alderson
authors.forename: I
authors.initials: I
authors.lastname: Pastan
authors.forename: S
authors.initials: S
authors.lastname: Cheng
mesh_terms: D000345:Affinity Labels; D002462:Cell Membrane / Q000378:metabolism; D002793:Cholic Acids / Q000494:pharmacology; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D008970:Molecular Weight; D010455:Peptides / Q000032:analysis; D010920:Placenta / Q000032:analysis*; D011247:Pregnancy; D011956:Receptors, Cell Surface / Q000302:isolation & purification*; D011988:Receptors, Thyroid Hormone; D012995:Solubility; D013963:Thyroid Hormones / Q000502:physiology; D014357:Trypsin / Q000494:pharmacology
chemical_list: D000345:Affinity Labels; D002793:Cholic Acids; D007457:Iodine Radioisotopes; D010455:Peptides; D011956:Receptors, Cell Surface; D011988:Receptors, Thyroid Hormone; D013963:Thyroid Hormones; D014357:Trypsin; C028213:3-((3-cholamidopropyl)dimethylammonium)-1-propanesulfonate