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DIO3

Meaning

DIO3, or Deiodinase Type 3, is a critical enzyme in the thyroid hormone metabolic pathway that functions exclusively as an inactivator of active thyroid hormones, serving a vital protective role against excess hormone action, particularly in sensitive tissues. This enzyme catalyzes the inner-ring deiodination of thyroxine (T4) to reverse T3 (rT3) and, crucially, the inner-ring deiodination of the active triiodothyronine (T3) to the inactive diiodothyronine (T2). DIO3 is highly expressed in the placenta, brain, and developing tissues, where it establishes a protective metabolic barrier to shield these areas from high T3 concentrations. Its expression is often induced in pathological states, such as hypoxia or certain tumors, as a mechanism to reduce cellular metabolic demand.