Binding of L-triiodothyronine to isolated rat liver and kidney nuclei under various circumstances.
Triiodothyronine (T3) is specifically bound by nuclei from rat liver and kidney. Binding of T3 at 37 degrees C reaches its maximum at 30 min. In the presence of EDTA (to remove Mg2+) T3 binds to a class of binding sites with an estimated equilibrium association constant (Ka) of 3.3 x 10(10) M(-1) and a maximal binding capacity (MBC) of 3.8 fmol T3/100 mug DNA. In the presence of MgCl2 T3 binds to a second class of binding sites with an estimated Ka of 4.8 x 10(8) M(-1) and a MBC of 123 fmol/100 mug DNA. Among the analogues tested, binding - relative to T3 - of D-T3, triiodothyoacetic acid and desamino-T3 is the same for both classes of binding sites, but relative affinity of thyroxine, D-T4, tetraiodothyroacetic acid and desamino-T4 is 2.5 to 6 times higher for the second class of binding sites than for the first class. The presence of a cytosol binding protein is not a prerequisite for binding of T3 to the nucleus.
D000818:Animals; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004492:Edetic Acid / Q000494:pharmacology; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D011485:Protein Binding; D051381:Rats; D014284:Triiodothyronine / Q000378:metabolism*
D014284:Triiodothyronine; D004492:Edetic Acid; D008274:Magnesium