title: Different thyroid hormone-deiodinating enzymes in tilapia (Oreochromis niloticus) liver and kidney.
abstract: Enzymes catalyzing the outer ring deiodination (ORD) of iodothyronines are important for the regulation of thyroid hormone bioactivity. We have studied ORD of thyroxine (T4) and 3,3',5'-triiodothyronine (rT3) in liver and kidney microsomes of fish, i.e. tilapia (Oreochromis niloticus). Tilapia kidney contains an enzyme which resembles the mammalian selenoenzyme type I iodothyronine deiodinase (ID-I) with respect to substrate preference (rT3 > T4) and high (approximately microM) Km values, but is much less sensitive to selenocysteine (Sec)-targeted inhibitors, including 6-propyl-2-thiouracil (PTU). In contrast, tilapia liver contains an enzyme very similar to mammalian type II deiodinase (ID-II) with respect to substrate preference (T4 > rT3), low (approximately nM) Km values, and lack of sensitivity to Sec inhibitors.
authors: Laboratory of Comparative Endocrinology, Catholic University of Leuven, Belgium.
authors: K
authors: K
authors: Mol
authors: E
authors: E
authors: Kaptein
authors: V M
authors: VM
authors: Darras
authors: W J
authors: WJ
authors: de Greef
authors: E R
authors: ER
authors: Kühn
authors: T J
authors: TJ
authors: Visser
mesh_terms: D000818:Animals; D001921:Brain / Q000201:enzymology; D007453:Iodide Peroxidase / Q000302:isolation & purification / Q000378:metabolism*; D007527:Isoenzymes / Q000302:isolation & purification / Q000378:metabolism*; D007668:Kidney / Q000201:enzymology*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D009928:Organ Specificity; D051381:Rats; D013045:Species Specificity; D013347:Subcellular Fractions / Q000201:enzymology; D017210:Tilapia / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; D007453:Iodide Peroxidase