Characterization of Iodothyronine Outer Ring and Inner Ring Deiodinase Activities in the Blue Tilapia,Oreochromis Aureus

Saturation of the tilapia kidney deiodinase required somewhat higher rT3 concentrations than rat D1, these results suggest that rT3 outer ring deiodination in tilapia kidney is catalyzed by a high-Km, rT3-preferring, D1-like enzyme

Koen A. Mol; Serge van der Geyten; Veerle M. Darras; Theo J. Visser; Eduard R. Kühn


Scholarcy highlights

  • I iodothyronine deiodinase but is much less sensitive to inhibition by propylthiouracil, iodoacetic acid, and aurothioglucose
  • ENZYMATIC deiodination of thyroid hormone has been studied in fish for more than two decades, but the presence of both outer ring and inner ring deiodination in fish has been demonstrated only recently
  • Results rT3 outer ring deiodination activity was found in tilapia kidney and to a lesser extent in liver and brain, the activities of the two latter tissues were near the detection limit of the assay
  • Formation of IϪ, but not T3, from T4 was found in these tissues, suggesting that IϪ release was due to a nonenzymatic process
  • The Km values of the tilapia deiodinase activities for their preferred substrates were in the same range as those of the corresponding rat enzymes, the apparent Km for rT3 ORD by tilapia kidney was approximately six times higher than the corresponding value in rat liver
  • ORD of T4 is observed in tilapia testis, but it remains to be established if this represents a separate deiodinase activity
  • The tilapia kidney enzyme and rat D1 display very similar affinities for the different iodothyronines, they exhibit strikingly different susceptibilities to inhibition by PTU, iodoacetic acid, and ATG

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