Diiodotyrosine (DIT) is a precursor in the production of thyroid hormone, and results from iodization of monoiodotyrosine at the other meta- position on the phenol ring.

DIT is a modulator of the enzyme thyroid peroxidase (which is involved in the production of thyroid hormones).

[1] Triiodothyronine is formed, when diiodotyrosine is combined with monoiodotyrosine (in the colloid of the thyroid follicle).

Two molecules of DIT combine to make the thyroid hormone thyroxine ('T4' and 'T3').

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