title: In vitro binding of 3,5-di-iodo-L-thyronine to rat liver mitochondria.
abstract: In this study we have demonstrated that specific binding sites for 3,5-di-iodo-L-thyronine (3,5-T2) can be detected in rat liver mitochondria. After incubation with the homogenate, liver mitochondria bound only a small portion of [3,5-125I]T2. The addition of a 100-fold excess of unlabelled 3,5-T2 caused the displacement of on average 50-60% of the [3,5-125I]T2 bound. Specific binding of 3,5-T2 to rat liver mitochondria occurred rapidly; a maximum was achieved after 5 min. Maximal binding was obtained at 37 degrees C, while at 0 degrees C and 20 degrees C the values were only slightly lower. Binding was maximal at pH 7.0; mean (+/- S.E.M.) values for the apparent association constant and the binding capacity (calculated at pH 7.0, 0 degrees C and after 30 min of incubation) were 0.5 +/- 0.04 x 10(8) M-1 and 0.4 +/- 0.04 pmol/mg mitochondrial protein respectively. The specificity of binding, examined in competition studies, followed the order: 3,5-T2 > 3,3'-di-iodo-L-thyronine > 3',3,5-tri-iodo-L-thyronine > thyroxine. Other iodothyronines (3',5'-di-iodo-L-thyronine, 3,5-di-iodo-D-thyronine, 3,3',5'-tri-iodo-L-thyronine, 3-iodo-L-thyronine and 3,5-di-iodothyroacetic acid) showed little or no competition. This suggests that the specific 3,5-T2 binding sites could be of biological relevance with respect to the understanding of the mechanism of physiological action of thyroid hormones at the cellular level.
authors.affiliation: Department of General and Environmental Physiology, University of Naples, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Goglia
authors.forename: A
authors.initials: A
authors.lastname: Lanni
authors.forename: C
authors.initials: C
authors.lastname: Horst
authors.forename: M
authors.initials: M
authors.lastname: Moreno
authors.forename: R
authors.initials: R
authors.lastname: Thoma
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D002458:Cell Fractionation; D004104:Diiodothyronines / Q000378:metabolism*; D004229:Dithiothreitol / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D008297:Male; D008930:Mitochondria, Liver / Q000378:metabolism*; D011441:Propylthiouracil / Q000494:pharmacology; D011485:Protein Binding; D051381:Rats; D017208:Rats, Wistar; D011988:Receptors, Thyroid Hormone / Q000378:metabolism; D013696:Temperature
chemical_list: D004104:Diiodothyronines; D011988:Receptors, Thyroid Hormone; C030103:3,5-diiodothyronine; D011441:Propylthiouracil; D000255:Adenosine Triphosphate; D004229:Dithiothreitol