CAPTION : The two most active thyroid hormones, triiodothyronine (T3) (left) and thyroxine (T33) (right contain iodine atoms typical of the thyroid hormones. (click each image for 3-D interactive animation) CREDIT : ChemIDPlus, National Library of Medicine.
Remember that hormone is still tied up in molecules of thyroglobulin - the task remaining is to liberate it from the scaffold and secrete free hormone into blood. Thyroid hormones are excised from their thyroglobulin scaffold by digestion in lysosomes of thyroid epithelial cells.
If a di-iodotyrosine and a mono-iodotyrosine are coupled together, the result is the formation of tri-iodothyronine (T3). From the perspective of the formation of thyroid hormone, the major coupling reaction is the di-iodotyrosine coupling to produce T4.
Their actions and influence are so wide-ranging that vertebrates cannot live without them. Among other things, thyroid hormones specifically affect brain development; heart rate; lung function; blood function; bone growth; steroid hormone production and breakdown; sugar, fat, and protein breakdown; and some immune processes.
Thyroid hormones. (click each image for 3-D interactive animation) CREDIT : ChemIDPlus, National Library of Medicine. Thyroid Synthesis The most common.
In essence, the free-floating thyroid hormone is filtered from the blood into the liver, quickly coated with sugar, and excreted out of the body. Thyroid hormone levels fall, and the thyroid gland balloons into a goiter.
The hormones start hair growth in rodents, sheep, and other mammals. They also initiate amphibian metamorphosis that transforms tadpoles into frogs. A delicate balance of thyroid hormones ensures health in children and adults.
Thyroid Hormone Synthesis General The first step in the synthesis of thyroid hormones is the organification of iodine. Iodide is taken up, converted to iodine, and then condensed onto tyrosine residues which reside along the polypeptide backbone of a protein molecule called thyroglobulin.
The T3 and T4 released from the thyroid by proteolysis reach the bloodstream where they are bound to thyroid hormone binding proteins. The major thyroid hormone binding protein is thyroxin binding globulin (TBG) which accounts for about 75 of the bound hormone.
Thyroid peroxidase catalyzes two sequential reactions: Iodination of tyrosines on thyroglobulin (also known as "organification of iodide. Synthesis of thyroxine or triiodothyronine from two iodotyrosines. Through the action of thyroid peroxidase, thyroid hormones accumulate in colloid, on the surface of thyroid epithelial cells.
Once inside the cell, iodide is transported into the lumen of the follicle along with thyroglobulin. Fabrication of thyroid hormones is conducted by the enzyme thyroid peroxidase, an integral membrane protein present in the apical (colloid-facing) plasma membrane of thyroid epithelial cells.