Characterization of the 3,3',5-triiodo-L-thyronine-binding site on plasma membranes from human placenta
The binding of (/sup 125/I)T3 to sites on human placenta plasma membranes was characterized, and the binding site was solubilized after affinity labeling with N-bromoacetyl-(/sup 125/I)T3 (BrAc(/sup 125/I)T3). Two classes of T3-binding sites were detected. One class has a high affinity (K /sub d/ = 2.0nM) and a low capacity (approximately 320 fmol/mg protein); the other has a low affinity (K /sub k/ = 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 (/sup 125/I)T3. The affinity labeling ligand BrAc(/sup 125/I)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(/sup 125/I)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.
- OSTI ID:
- 5021556
- Journal Information:
- Endocrinology; (United States), Vol. 6
- Country of Publication:
- United States
- Language:
- English
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RECEPTORS
BIOCHEMICAL REACTION KINETICS
LABELLING
TRIIODOTHYRONINE
CELL MEMBRANES
ELECTROPHORESIS
GEL PERMEATION CHROMATOGRAPHY
IN VITRO
IODINE 125
MOLECULAR WEIGHT
PLACENTA
PREGNANCY
THYROID HORMONES
TRYPSIN
WOMEN
ANIMALS
BETA DECAY RADIOISOTOPES
CELL CONSTITUENTS
CHROMATOGRAPHY
DAYS LIVING RADIOISOTOPES
ELECTRON CAPTURE RADIOISOTOPES
ENZYMES
FEMALES
FETAL MEMBRANES
HORMONES
HYDROLASES
INTERMEDIATE MASS NUCLEI
IODINE ISOTOPES
ISOTOPES
KINETICS
MAMMALS
MAN
MEMBRANES
NUCLEI
ODD-EVEN NUCLEI
PEPTIDE HORMONES
PEPTIDE HYDROLASES
PRIMATES
RADIOISOTOPES
REACTION KINETICS
SEPARATION PROCESSES
SERINE PROTEINASES
VERTEBRATES
550201* - Biochemistry- Tracer Techniques