Presence of Iodinated Amino Acids in Unhydrolyzed Thyroid and Plasma

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Abstract
Adult female rats kept on a low iodine diet were sacrificed and the thyroids and blood plasma removed 48 hrs. after the subcut. injn. of 100[mu]c of radioiodine in the form of NaI131. Butanol extracts of plasma and thyroids of exptl. animals were evaporated to dryness, and the residues were dissolved in water and analyzed by 2-dimensional paper chroma-tography using both color development and radioautograph methods with or without addition of DL-thyroxine, DL-diiodothyronine, DL-diiodotyrosine, or DL-monoiodotyrosine as carriers. Chroma-tograms revealed the presence of 8 radioactive compounds; 5 of these were identified as iodine, thyroglobulin, thyroxine, diiodo-tyrosine, and monoiodotyrosine; the remaining 2 were unidentified. In the blood plasma practically all of the butanol-extractable radioactivity was present as thyroxine, with a small amt. of diiodotyrosine and iodine. Analysis of whole plasma by radiography of 2-dimensional buffer chromatograms showed the position of the radioactive material to correspond with that of the plasma proteins. Although thyroxine solns. showed no movement from the origin under these conditions, radioactive thyroxine dissolved in nonradioactive plasma was displaced along with the plasma proteins and gave a pattern very similar to that of radioactive plasma itself. It was concluded that thyroxine, after its release from thyroglobulin by proteolytic enzymes in the thyroid follicles, circulates in combination with plasma proteins. The complex thus formed can be split with butanol, and reconstituted in vitro.

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