Nuclear triiodothyronine receptor of human adipose tissue.
L-Triiodothyronine induces malic enzyme in explants from human adipose tissue. Consequently, we looked for the presence of receptors for L-triiodothyronine in nuclei isolated from human adipose tissue. The binding of 125I-triiodothyronine by the nuclei was time- and temperature-dependent. At 37 degrees C binding reached a steady state after 60 minutes. Dithiothreitol enhanced total binding and suppressed nonspecific binding. Scatchard analysis showed the presence of a single class of binding sites. The apparent association constant, Ka, was 0.13 +/- 0.03 X 10(10) M-1, the maximal binding capacity 2.20 +/- 0.81 pmol/mg DNA (mean +/- SD, n = 7) and the number of binding sites 8,000/nucleus. L-Triiodothyronine and D-triiodothyronine had equal affinity to the nuclear receptor; triiodothyroacetic acid had three times higher affinity. L- and D-thyroxine had 8% and 12%, respectively, and tetraiodothyroacetic acid had 19% affinity compared to that of L-triiodothyronine. Reverse triiodothyronine was a weak competitor. Digestion of nuclei with micrococcal nuclease abolished specific binding. These results show that nuclei from human white adipose tissue possess high affinity receptors for L-triiodothyronine, which are associated with nuclear chromatin. It is likely that induction of malic enzyme in human adipose tissue by L-triiodothyronine is mediated by the nuclear receptors.
Cronrath
C M
CM
Institut fuer Klinische Biochemie, Universitaet Bonn, Federal Republic of Germany.
Rao
G S
GS
Rao
M L
ML
D000273:Adipose Tissue / Q000032:analysis*; D000328:Adult; D002467:Cell Nucleus / Q000032:analysis*; D004229:Dithiothreitol / Q000494:pharmacology; D005260:Female; D006801:Humans; D008836:Micrococcal Nuclease / Q000494:pharmacology; D008875:Middle Aged; D011988:Receptors, Thyroid Hormone / Q000032:analysis* / Q000378:metabolism; D013696:Temperature; D013997:Time Factors
D011988:Receptors, Thyroid Hormone; D008836:Micrococcal Nuclease; D004229:Dithiothreitol