MEDICAL PHYSIOLOGY

Detailed explanation-1: -T4 is converted into T3, the active form of thyroid hormone, by two enzymes called deiodinases. People with hypothyroidism are treated with a synthetic T4 hormone, which the enzymes convert to T3. This treatment is usually effective, but some people continue to have symptoms even after treatment.

Detailed explanation-2: -T4 is converted to the active T3 form by deiodination, removal of an iodide from the outer phenolic benzene ring by selenium-containing enzymes, deiodinase enzymes D1 or D2.