Thyroid hormone synthesis
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Synthesis of thyroid hormones.
Reference:
- Chapter 48, "SYNTHESIS OF THYROID HORMONES" in: Walter F., PhD. Boron () Medical Physiology: A Cellular And Molecular Approach, Elsevier/Saunders, S. 1,300 ISBN: 1-4160-2328-3.
Explanation
- Thyroglobulin is synthesized in the rough endoplasmic reticulum and follows the secretory pathway to enter the colloid in the lumen of the thyroid follicle by exocytosis.
- Meanwhile, a sodium-iodide (Na/I) symporter pumps iodide (I-) actively into the cell, which previously has crossed the endothelium by largely unknown mechanisms.
- This iodide enters the follicular lumen from the cytoplasm by the transporter pendrin, in a purportedly passive manner.[1]
- In the colloid, iodide (I-) is oxidized to iodine (I0) by an enzyme called thyroid peroxidase.
- Iodine (I0) is very reactive and iodinates the thyroglobulin at tyrosyl residues in its protein chain (in total containing approximately 120 tyrosyl residues).
- In conjugation, adjacent tyrosyl residues are paired together.
- The entire complex re-enters the follicular cell by endocytosis.
- Proteolysis by various proteases liberates thyroxine and triiodothyronine molecules
- Efflux of thyroxine and triiodothyronine from follicular cells, which appears to be largely through monocarboxylate transporter (MCT) 8 and 10,[2][3] and entry into the blood.
Additional references for details
- ↑ How Iodide Reaches its Site of Utilisation in the Thyroid Gland – Involvement of Solute Carrier 26A4 (Pendrin) and Solute Carrier 5A8 (Apical Iodide Transporter) - a report by Bernard A Rousset. Touch Brieflings 2007
- ↑ (2008). "Effective Cellular Uptake and Efflux of Thyroid Hormone by Human Monocarboxylate Transporter 10". Molecular Endocrinology 22 (6): 1357–1369. DOI:10.1210/me.2007-0112. ISSN 0888-8809.
- ↑ (2011). "Molecules important for thyroid hormone synthesis and action - known facts and future perspectives". Thyroid Research 4 (Suppl 1): S9. DOI:10.1186/1756-6614-4-S1-S9. ISSN 1756-6614.
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