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 fiver mitochondria occurred rapidly; a maximum was achieved after 5 min. Maximal binding was obtained at 37°C, while at 0°C and 20°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°C and after 30 min of incubation) were 0.5 ± 0.04 x 108 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 physibiogical action of thyroid hormones at the cellular level.
IN-VITRO BINDING OF 3,5-DI-IODO-L-THYRONINE TO RAT-LIVER MITOCHONDRIA
LANNI, Antonia;
1994
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 fiver mitochondria occurred rapidly; a maximum was achieved after 5 min. Maximal binding was obtained at 37°C, while at 0°C and 20°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°C and after 30 min of incubation) were 0.5 ± 0.04 x 108 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 physibiogical action of thyroid hormones at the cellular level.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.