[Triiodothyronine binding by the liver nuclei and mitochondria]

The binding of I125-triiodothyronine by male thyroidectomized rat liver nuclei and mitochondria in vivo and in vitro was studied. Labeled triiodothyronine was bound by the liver nuclei and mitochondria proteins. 90% radioactivity was bound by the nuclear nonhistone proteins. The binding of I125-triiodothyronine to the nuclei and mitochondria protein receptors was inhibited by unlabeled triiodothyronine and ICl. It is suggested that aromatic amino acids serve as the binding sites of the protein receptors, and that iodine atoms in the thyroid hormone molecules participated directly in the binding process.