PRESENCE AND BIOSYNTHESIS OF THYROID HORMONES IN A TUNICATE, CIONA INTESTINALIS (in French)
A tunicate, Ciona intestinalis L., binds very actively I/sup 131/-ions. The labeled iodine is preferentially located (75%) in the external layer of the tunic. The iodine metabolism is there chiefly oriented toward the biosynthesis of iodothyronines (thyroid hormones). The presence of free thyroxine and 3,5,3'- triiodothyronine in the tissues of Ciona has been established. Biogenesis of 3,5,3'-triiodothyronine and thyroxine proceeds chiefly in the tunic, in which three fractions of iodoproteins were characterized. Two of these, one soluble in various media, the other bound to insoluble structure, contain 3,5,3'- triiodothyronine, thyroxine and their precursors, 3-monoiodo- and 3,5- diiodotyrosine. The four iodinated amino acids are freed from these proteins by action of pancreatic proteinases and papain. An insoluble residue of iodinated scleroprotein, not hydrolyzed by proteinases, does not take part to endocrine activity; 3-monoiodotyrosine and 3,5-diiodotyrosine only are found in the products of its alkaline hydrolysis. The mechanism of hormonogenesis seems identical in all chordata (urochordata, cephalochordata, and vertebrates). As thyroid hormones are found in these and not in invertebrates lower than urochordata, their appearance in this subphylum can be considered as a fundamental step of biochemical evolution of the thyroid function. Biosynthesis of iodothyronines is characteristic of chordata. It proceeds in all of these, including protochordata, by the same mechanism, but under conditions submitted to the evolution of the secretory tissue through a series of steps, the last of which is the thyroid follicle of vertebrates. (auth)
- Research Organization:
- Universita, Naples
- NSA Number:
- NSA-16-031452
- OSTI ID:
- 4778991
- Journal Information:
- Biochim. et Biophys. Acta, Journal Name: Biochim. et Biophys. Acta Vol. Vol: 63
- Country of Publication:
- Country unknown/Code not available
- Language:
- French
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