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The chemical purity of the iodine in our Iodine
is greater than or = 99.8%. We are more concerned
about the purity than the actual source. Iodine
from seaweed may possibly contain impurities found
in the ocean such as arsenic, bromine in quantities
that are not desirable or healthy.
Iodine Metabolism In the Thyroid
The major function of the gland is to concentrate
iodine, and to synthesize thyroxine (T 4 ) or triiodothyronine
(T 3 ). There is always about 20-50 mg of iodine
in the body; 8 mg is in the thyroid. The supply
may be variable. Iodine comes from water and food,
but is also absorbed by intact skin and lungs. Throughout
the world, the intake varies. 1 mg is needed per
week, or about 50 mg/year. Diet under normal circumstances
contains at least 150 micrograms daily.
The iodine pump (iodide trapping) gets the ion
into the thyroid. It works against the concentration
gradient which is at least 1 (blood) to 25 (gland).
The pump is activated by pituitary TSH. ATP is utilized
as a source of energy. Excess iodine in the gland
inhibits the thyroid hormone synthesis.
Thyroid Hormone Synthesis
Iodide is first oxidized either into nascent iodine
Io or I 3- The enzyme peroxidase is necessary as
well as hydrogen peroxide. Then, iodine is attached
to tyrosine which is the precursor of the thyroid
hormones. Monoiodotyrosine and diiodotyrosine are
formed by tyrosine iodinase.
Then, two molecules of iodinated tyrosine are coupled
into T 3 and T 4 . T 3 is four times as potent as
T 4 . About three quarters of the iodinated tyrosine
never becomes thyroid hormones. They may be released
from thyroglobulin and deiodinated by a deiodinase
enzyme. About 90% of hormone produced is thyroxin.
The hormones are formed within a globulin molecule
in the thyroid and stored as thyroglobuline (MW
about 670,000), where there are about 3 molecules
of thyroxine and 1 molecule of T 3 per molecule
of thyroglobulin. About 2 to 3 months of supply
is stored in the gland.
Hormone release and transport
Thyroid hormone secretory pathway is composed of
three steps:
* The internalization and intracellular transport
of thyroglobulin,
* Proteolytic processing of the prohormone,
* Cellular handling and release of T 4 and T 3 .
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