THE METABOLISM OF IODOTYROSINES. III. DI-IODOTYROSINE DESHALOGENATING ACTIVITY OF HUMAN THYROID TISSUE

Abstract

Di-Iodotyrosine is readily deiodinated by tissue slices from many organs. Hartmann (1) observed that up to 25 per cent of di-iodotyrosine was deiodinated by dog liver slices. Deshalogenation was demonstrated to lesser degree in various other tissues, including kidney and thyroid from the dog, rabbit, guinea pig and rat. These observations have been criticized for technical reasons and extended by Roche and his colleagues (2, 3) using I131-labeled mono- and di-iodotyrosine as substrate. Deiodination was observed in the thyroid of the sheep and rabbit, kidney of the dog, and in other tissues. In the lung of the rabbit and dog, there was no activity. This deshalogenating enzyme has been concentrated and characterized by Roche et al. (3). It is specific for the halogen derivatives of tyrosine, but does not deshalogenate thyroxine or tri-iodothyronine.