Some Properties of the Stimulatory Effect of Thyroid Hormones on Amino Acid Transport by Embryonic Chick Bone

Abstract

Some charac-teristics of the stimulation by thyroid hormones of the intracellular accumulation of methionine and cycloleucine by embryonic chick bones are described. The stimulation by triiodothyroinine exceeded that of L-thyroxine. 3,3''-Diiodothyonine was as effective as L-thyroxine, which was more active than 3,5-diiodothyronine or D-thyroxine. Diiodothyro-sine, thyronine and inorganic iodide were inactive at comparable concentrations. Stimulation of the accumulation of methionine appeared to be immediate. The effect was not accompanied by a stimulation of amino acid incorporation and was not inhibited by puromycin or by actinomycin D prior to the inhibition by these antibiotics of transport per se. Chelation of metals by ethylenediamine tetraacetate did not produce similar effects. Stimulation of the accumulation of free methionine by costal and xiphoid cartilage of mature thyroidectomized rats was also observed.