What is the Origin of Thyroxine Triiodothyronine Conversion?

The nomenclature is derived from the chemical structures: T4 has four iodine atoms, and T3 has three. The understanding of peripheral conversion as a primary regulatory step emerged in the 1970s, shifting the focus from T4 as the sole active hormone. The term describes the physiological activation of the thyroid prohormone.

What is the Mechanism of Thyroxine Triiodothyronine Conversion?

The conversion is mechanistically controlled by three types of iodothyronine deiodinases (D1, D2, and D3). Deiodinase 1 and 2 remove an iodine atom from the outer ring of T4 to produce active T3, increasing metabolic signaling. Deiodinase 3 removes an iodine from the inner ring, creating reverse T3 (rT3), which is biologically inactive and serves as a clearance pathway. This enzymatic regulation allows tissues to locally control the availability of active T3.

Thyroxine Triiodothyronine Conversion ∞ Area

Thyroxine Triiodothyronine Conversion

Meaning

The critical metabolic process in which the prohormone thyroxine (T4), secreted primarily by the thyroid gland, is converted into the biologically active hormone triiodothyronine (T3) by the removal of a single iodine atom. This conversion is predominantly catalyzed by deiodinase enzymes in peripheral tissues like the liver, kidney, and muscle, and is essential because T3 is significantly more potent at the cellular receptor level than T4. Clinical assessment of this conversion efficiency is key to understanding tissue-level thyroid function.