Sitat Opprinnelig skrevet av Mod Vis post
Iodine and Evolution.
Iodine and Evolution
Venturi S
Published in Italian online: February 8, 2004

SUMMARY
The authors report their hypothesis on the antioxidant role of iodine in the evolution of life on the earth. Iodine is the most electron rich of the essential elements in the animal diet, and as iodide (I-) enters in the cells by an iodide transporter. Iodide, which acts as primitive electron donor by peroxidase enzymes, seems to have an ancestral antioxidant function in all iodide-concentrating cells from primitive marine algae to more recent terrestrial vertebrates.

Thyroxine and iodothyronines seem also to have an antioxidant activity, by deiodinase enzymes, which are donors of iodides and indirectly of electrons. Thyroid cells phylogenetically derived from primitive gastroenteric cells, which during evolution, migrated and specialized in uptake and storage iodine-compounds in the new follicle, as reservoir of iodine, for a better adaptation of modern vertebrates to iodine deficient terrestrial environment.

INTRODUCTION
Iodine (I) is the most electron rich of the essential elements in the animal diet, and as iodide (I-) enters in the cells. Inorganic iodide is necessary for all living cells, but only the vertebrates have a thyroid gland and its iodinated hormones. In humans, the total amount of iodine is about 25-50 mg and about 60-70 % of total iodine is non-hormonal which is concentrated in non-follicular extrathyroidal tissues, where its biological role is still unknown. Sodium iodide symporter (NIS) of iodide pump, which was in 1996 genetically characterised and cloned (1, 2), is a transmembrane protein which actively transports iodide into the cells.

Extrathyroidal NIS, more primitive than the thyroidal one, have a lower affinity for iodide and does not respond to more evolute TSH (Thyrotropin). We believe that the mechanism of iodide-pump (and NIS) is very ancient in the cells, and for this reason, there is a rather surprising lack of specificity for the anions. The pump is not able to distinguish iodide from other anions of similar atomic or molecular size, which may act as pseudo-iodides: thiocyanate, cyanate, nitrate, pertechnetate, perchlorate, [fluoride/red.]etc. On the contrary, this pump is partially able to defend itself and the cell from toxic I-excess (Wolff-Chaikoff effect) (3, 4).

IODINE AND EVOLUTION
Over three billion years ago, blue-green algae (Cyanobacteria), which are the most primitive oxygenic photosynthetic organisms, ancestors of multicellular eukaryotic algae that contain the highest amount of iodine (1-4 % of dry weight) and peroxidase enzymes, were the first living cells to produce poisonous oxygen in the atmosphere (5, 6, 7). Therefore algal cells required a protective antioxidant action in which iodides with peroxidase seem to have had this specific role (8, 9, 10).

In fact iodides are greatly present and available in sea-waters, where algal phytoplankton, the basis of marine food-chain, acts as a biological accumulator of iodides, selenium (and n-3 fatty acids). The sea is rich in iodine, about 60 micrograms (ug) per litre, since this is where most of the iodine removed and washed away from the soil accumulated by the glaciations ages.


Read more / les mer... (Sites.google.com The link is to the English summary, as well as the Italian article complete with pictures and diagrams.)