What is the Origin of Deiodinase Type 3?

The enzyme's discovery is part of the broader elucidation of the thyroid hormone metabolic cascade, which involves three main deiodinase types (D1, D2, and D3), each with distinct tissue distribution and functions. D3 is uniquely characterized by its role as a physiological "brake," highly expressed in tissues like the placenta and brain during development, and pathologically upregulated in certain disease states.

What is the Mechanism of Deiodinase Type 3?

D3's primary mechanism is the removal of an iodine atom from the inner ring of the iodothyronine molecule. In the context of hormonal health, D3 activity is often upregulated in conditions of systemic stress or tissue hypoxia, acting to conserve energy by locally reducing thyroid-mediated metabolic rate. Elevated D3 expression can lead to localized or systemic hypothyroidism-like states, even when circulating T4 levels appear normal.

Deiodinase Type 3 ∞ Area

Deiodinase Type 3

Meaning

Deiodinase Type 3 (D3) is a selenocysteine-containing enzyme (iodothyronine deiodinase) that plays a critical role in thyroid hormone metabolism by catalyzing the inner-ring deiodination of thyroxine (T4) and triiodothyronine (T3). This specific action converts the active hormones into inactive metabolites, reverse T3 (rT3) and T2, effectively serving as a major mechanism for local hormone inactivation and protection against excess thyroid signaling.