Deiodinase T4 to T3 — FRCA Primary MCQ

Instant feedback + full explanation. One question, done properly.

HardPhysiology - Endocrine & MetabolicDeiodinase T4 to T3FRCA Primary

Which enzyme family catalyses peripheral conversion of thyroxine (T4) to triiodothyronine (T3)?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: A — Iodothyronine deiodinase enzymes in peripheral tissues

The best answer is “Iodothyronine deiodinase enzymes in peripheral tissues”. Type 1 and type 2 iodothyronine deiodinases convert T4 to biologically active T3 in peripheral tissues. Thyroid peroxidase is involved in hormone synthesis within the thyroid gland; COMT, monoamine oxidase and carbonic anhydrase have unrelated physiological roles.

Reference: RCoA, Primary FRCA Syllabus: https://rcoa.ac.uk/sites/default/files/documents/2026-01/Primary-FRCA-Syllabus.pdf