Some Characteristics of the Sheep Thyroid Gland System for Incorporating Amino Acids Into Protein

Abstract

The ability of sheep thyroid glands to incorporate the ¹⁴C of a variety of amino acids uniformly labeled with ¹⁴C into protein was studied in: (a) slices and (b) dispersed cells obtained by the continuous-flow trypsinization technique and cultured as monolayers. In slices, the ¹⁴C of the protein formed from valine ¹⁴C was located predominantly in mitochondrial and microsomal fractions. Addition of glucose, pyruvate, succinate or a-ketoglutarate to the incubation medium did not enhance incorporation of leucine-¹⁴C into protein by sheep thyroid slices. Thyrotropic hormone, added in vitro, had no effect on incorporation of leucine-¹⁴C into protein or on the uptake of ¹⁴C of α-amino isobutyric acid-l-¹⁴C by thyroid slices. Analysis of N- and C-terminal groups of ¹⁴C-proteins isolated from thyroid slices or cells incubated with the ¹⁴C-amino acids indicated that the incorporation took place predominantly at the interior sites of the protein molecules. Carbon from aspartate was incorporated into proteins by thyroid slices and cells not only in the form of aspartate but also as glutamate and alanine; similar transformations also occurred with alanine ¹⁴C and glutamate ¹⁴C. Interconversion of serine and glycine was demonstrated in sheep thyroid slices. Other metabolic interconversions of amino acids are also shown to occur in thyroid tissue. (Endocrinology74: 468, 1964)