Characterization of the 3,3',5-triiodo-L-thyronine-binding site on plasma membranes from human placenta

Endocrinology. 1985 Jun;116(6):2621-30. doi: 10.1210/endo-116-6-2621.


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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Affinity Labels
  • Cell Membrane / metabolism
  • Cholic Acids / pharmacology
  • Female
  • Humans
  • In Vitro Techniques
  • Iodine Radioisotopes
  • Molecular Weight
  • Peptides / analysis
  • Placenta / analysis*
  • Pregnancy
  • Receptors, Cell Surface / isolation & purification*
  • Receptors, Thyroid Hormone
  • Solubility
  • Thyroid Hormones / physiology
  • Trypsin / pharmacology


  • Affinity Labels
  • Cholic Acids
  • Iodine Radioisotopes
  • Peptides
  • Receptors, Cell Surface
  • Receptors, Thyroid Hormone
  • Thyroid Hormones
  • Trypsin
  • 3-((3-cholamidopropyl)dimethylammonium)-1-propanesulfonate