Thyroxine 5-deiodinase

Thyroxine 5-deiodinase is an enzyme that plays a crucial role in the metabolism of thyroid hormones. It is responsible for the conversion of the prohormone thyroxine (T4) into the active hormone triiodothyronine (T3) by removing an iodine atom from the outer ring of the thyroxine molecule. This process is known as deiodination.

Function

Thyroxine 5-deiodinase is primarily found in the liver, kidney, and thyroid gland. It is one of three deiodinase enzymes that regulate the levels of thyroid hormones in the body. The other two enzymes are thyroxine 3-deiodinase and thyroxine 5'-deiodinase.

The primary function of thyroxine 5-deiodinase is to convert thyroxine into triiodothyronine. This conversion is essential because triiodothyronine is the more active form of thyroid hormone, exerting a greater effect on the body's metabolic rate, heart rate, and body temperature.

Clinical significance

Abnormalities in the function of thyroxine 5-deiodinase can lead to disorders of thyroid hormone metabolism. For example, a deficiency in this enzyme can result in a condition known as hypothyroidism, characterized by low levels of thyroid hormones in the body. Symptoms of hypothyroidism can include fatigue, weight gain, and depression.

Conversely, an excess of thyroxine 5-deiodinase can lead to hyperthyroidism, a condition characterized by high levels of thyroid hormones. Symptoms of hyperthyroidism can include weight loss, increased heart rate, and anxiety.

See also

• Thyroid hormone
• Thyroid function tests
• Thyroid disease

References

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