Type I iodothyronine deiodinase is an enzyme that in humans is encoded by the DIO1 gene. This enzyme is a type of iodothyronine deiodinase (/), which are enzymes involved in activating and deactivate thyroid hormones by removing iodine atoms from them (called deiodination). This form is distinct in being capable of both activation and inactivation, unlike type II iodothyronine deiodinase which can only activate () thyroid hormones, and type III iodothyronine deiodinase which can only deactivate () thyroid hormones.
Function
As an (outer ring) thyroxine 5-deiodinase, () the DIO1 enzyme is able to catalyze the following reaction:
L-thyroxine + AH2 → 3,3',5-triiodo-L-thyronine + iodide + A + H+
Which converts the less active thyroxine (T4) into the more active triiodothyronine (T3) hormone. It is also able to act as an (inner ring) thyroxine 5'-deiodinase, (), which means it is also able to catalyze:
L-thyroxine + AH2 → 3,3',5'-triiodo-L-thyronine + iodide + A + H+
Which instead produces reverse triiodothyronine (rT3).
Medical significance Certain variants in the DIO1 gene have been associated with unusually high levels of rT3 in blood tests, called Thyroid hormone metabolism, abnormal, 2 (THMA2). However, the effect of this on health, if any, remains unclear.
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