déiodinases

Deiodinases are a family of enzymes that play a crucial role in thyroid hormone metabolism. These enzymes are responsible for removing iodine atoms from thyroid hormones, a process known as deiodination. There are three main types of deiodinases: Type I (D1), Type II (D2), and Type III (D3).

Type I deiodinase is primarily found in the liver, kidneys, and thyroid gland. It converts the prohormone thyroxine (T4) into the more active hormone triiodothyronine (T3), and also inactivates T3. D1 activity is important for maintaining circulating levels of T3.

Type II deiodinase is located in the brain, pituitary gland, brown adipose tissue, and heart. Like D1, D2 converts T4 to T3, but it primarily regulates intracellular T3 levels in these specific tissues, responding to local demand.

Type III deiodinase acts as an inactivator of thyroid hormones. It converts both T4 and T3 into inactive forms, such as reverse T3 (rT3). D3 is particularly important during fetal development and in certain physiological states where thyroid hormone activity needs to be suppressed.

The activity of deiodinases is tightly regulated by various factors, including thyroid hormone levels themselves, selenium, and other nutritional and hormonal signals. Dysregulation of deiodinase activity can contribute to thyroid disorders. These enzymes are essential for maintaining appropriate thyroid hormone levels in different tissues and for responding to the body's metabolic needs.