Thyroid hormones are metabolized predominantly by deiodination.Which of the following statements are true of deiodinase D1?
1)It is present in high concentration in liver and kidney.
2)It is the main source of T₃ in hyperthyroid patients.
3)It converts T₄ to equimolar amounts of T₃ and rT₃.
4)Its activity is sensitive to changes in serum T₄ and T₃.

Question

Quizplus · Accepted Answer

There are 3 deiodinases which are known as D1, D2, and D3.D1 is present in high concentration in liver and kidney and converts T₄ to T₃ and rT₃ in equimolar quantities.This enzyme is the main source of T₃ in hyperthyroid patients and is inhibited by the antithyroid drug propylthiouracil.D2 is present in high concentration in muscle, brain, skin, and placenta.Although the activity of D1 is not sensitive to changes in serum T₄ and T₃, the activities of D2 and D3 are sensitive to these levels and change in a reciprocal manner to hormone concentration to maintain homeostasis.

Thyroid Hormones Are Metabolized Predominantly by Deiodination