ISSN:
1471-4159
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Abstract— 3,3′,5-Triiodothyronine (T3) inhibited L-[14C]leucine uptake into synaptosomes. Inhibition was competitive with a Ki of 3.1 × 10−5m. Hofstee plot revealed an inverted hyperbolic curve suggestive of a two carrier or carrier plus diffusion mediated system for amino acid uptake. Both the carrier mediated and diffusional components were inhibited by thyroid analogues. l-Thyroxine and analogues inhibited the incorporation of l-[14C] leucine into cerebral synaptosome protein. At 50 μm, the triiodo-compounds were more inhibitory than tetraiodo-〉3,5-triiodo-l-thyronine 〉3,3′,5-triiodothyropro-pionic〉 l-thyroxine 〉3,5-diiodo-l-tyrosine. Thyroid analogue inhibition was not seen in liver or brain mitochondrial protein synthesis. 3,3′,5-Triiodothyronine had no effect on respiratory control or 2,4-DNP stimulated synaptosome respiration supported by malate plus pyruvate. Ouabain did not inhibit [14C]leucine uptake into adult synaptosomes. There was synergistic inhibition of synaptosome protein synthesis by thyroid analogues in the presence of 0.2 mm-ouabain. 3,3′,5-Triiodothyronine had no effect on synaptosome fraction ATPase or Na-K ATPase. Addition of T3 induced further inhibition of synaptosome protein synthesis in the presence of either chloramphenicol (100μm) or cycloheximide (50μg/ml). [14C]Glycine uptake and incorporation into synaptosome protein was inhibited by 3,3′,5-triiodothyronine. There was no inhibition of [14C]proline uptake or incorporation.The above evidence and kinetic data strongly favor a selective competitive block in amino acid transport at the synaptosome membrane leading to a decreased rate of protein synthesis.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1471-4159.1977.tb10728.x
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