Identification of thyroid hormone receptors in rat liver nuclei by photoaffinity labeling with L-thyroxine and triiodo-L-thyronine
Photoaffinity labeling of rat liver nuclear extract with underivatized thyroid hormones was performed after incubation with 1 nM (3',5'-125I)thyroxine ((125I)T4) or (3'-125I)triiodothyronine (( 125I)T3) by irradiation with light above 300 nm. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the covalently photolabeled nuclear extract revealed four distinct hormone binding proteins of molecular masses 96, 56, 45, and 35 kilodaltons (kDa), respectively. Distribution of the hormone among these proteins was similar for T4 and T3. The 56- and 45-kDa proteins were the most prominently labeled. The specificity of the photoattachment of thyroid hormones to these nuclear proteins was verified by the irradiation of eight randomly chosen proteins and two proteins known to have thyroid hormone binding sites, human thyroxine binding globulin and bovine serum albumin. Only the latter two were photolabeled with (125I)T4. Competition studies performed by incubating nuclear extracts with (125I)T4 or (125I)T3 in the presence of increasing amounts of the corresponding unlabeled hormone (10-, 100-, and 1000-fold molar excess) demonstrated that (1) photoattachment of labeled T3 or T4 to the 56- and 45-kDa proteins was inhibited by 67-78% and 73-85%, respectively, after incubation with a 1000-fold molar excess of unlabeled hormone, (2) in the presence of lower molar excesses of the corresponding competitor (10- and 100-fold), photoattachment of labeled T3 or T4 to the 56- and 45-kDa receptors was gradually inhibited to a similar extent on both proteins, and (3) the 35- and 96-kDa proteins, although having thyroid hormone binding sites, display lower binding activities since the inhibition of photoattachment of labeled T3 or T4 by a 1000-fold molar excess of unlabeled hormone did not exceed 30-42% and 26-49%, respectively.
- Research Organization:
- National Institute of Arthritis, Bethesda, MD
- OSTI ID:
- 5882004
- Journal Information:
- Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 19; ISSN BICHA
- Country of Publication:
- United States
- Language:
- English
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59 BASIC BIOLOGICAL SCIENCES
AMINO ACIDS
ANIMALS
BETA DECAY RADIOISOTOPES
BODY
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CELL NUCLEI
CHEMICAL BONDS
CHEMICAL REACTIONS
DAYS LIVING RADIOISOTOPES
DIGESTIVE SYSTEM
ELECTRON CAPTURE RADIOISOTOPES
GLANDS
HORMONES
INTERMEDIATE MASS NUCLEI
IODINE 125
IODINE ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
LABELLED COMPOUNDS
LABELLING
LIVER
MAMMALS
MEMBRANE PROTEINS
MOLECULAR WEIGHT
NUCLEI
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC IODINE COMPOUNDS
ORGANS
PEPTIDE HORMONES
PHOTOCHEMICAL REACTIONS
PROTEINS
RADIOISOTOPES
RATS
RECEPTORS
RODENTS
THYROID HORMONES
THYROXINE
TRACER TECHNIQUES
TRIIODOTHYRONINE
VERTEBRATES