Letter | Published:

Transiodination of Proteins during Enzymic De-iodination of Thyroxine



DURING the enzymic de-iodination of thyroxine labelled with iodine-131, triiodothyronine and related compounds with tissue homogenates, a fraction of the radioactivity consistently appeared in a material of RF = 0 in various chromatographic systems1. The amount of ‘origin’ radioactive material found on chromatograms increased almost in parallel with the de-iodination of the substrate. With the identification of ferrous ions and flavin as activators for thyroxine dehalogenase2, the formation of this material was found to be dependent only on flavin derivatives. The nature of the ‘origin’ iodine-131 labelled material was studied with purified preparations of thyroxine dehalogenase3 ; it was found to be radioiodinated protein(s) present in the tissue enzymic extracts, as described below.

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  1. 1

    Tata, J. R., Rall, J. E., and Rawson, R. W., Endocrinol., 60, 83 (1957) ; Proc. Soc. Exp. Biol., N.Y., 95, 362 (1957).

  2. 2

    Tata, J. R., Biochim. Biophys. Acta, 35, 567 (1959).

  3. 3

    Tata, J. R., Biochem. J. (in the press).

  4. 4

    Saunders, B. C., and Stark, B. P., Tetrahedron, 4, 169 (1958).

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