Biomaterial Database

Comparison of kidney and brown adipose tissue iodothyronine 5'-deiodinases. 1987

J E Silva, and S Mellen, and P R Larsen

We have examined the influence of assay conditions on the 6-n-propyl-2-thiouracil (PTU) sensitivity of the iodothyronine 5'-deiodinase in brown adipose tissue (BAT) from hypothyroid rats. These results were compared with similar studies of 5'-deiodinase activity in kidney microsomes from euthyroid animals. Even though BAT microsomes contain largely type II (PTU-insensitive) deiodinase activity, the 5'-deiodination of T4 can be inhibited by PTU if the dithiothreitol (DTT) concentration in the assay is reduced to 5 mM or less. The apparent Ki for PTU of BAT microsomes was 4.3 mM at 5.0 mM DTT and 0.41 mM at 0.5 mM DTT. The kinetics of inhibition were noncompetitive. With kidney microsomes, PTU inhibition of rT3 5'-deiodination was both time and enzyme/substrate ratio dependent. For example, using 1 microgram microsomal protein, 2 nM rT3, and 5 mM DTT, the inhibitory effect of PTU was not maximal until 12 min after PTU addition. At stable reaction velocities PTU inhibition was uncompetitive, and the Ki was about 1 microM. Deiodination by kidney microsomes was completely inhibited by 50 microM PTU. Even though it is possible to inhibit the type II 5'-deiodinase activity with high concentrations of PTU (in the presence of low DTT concentrations), the deiodinase in kidney is about 1000-fold more sensitive to PTU. By these criteria the kidney microsome 5'-deiodinase is type I.

UI	MeSH Term	Description	Entries
D007453	Iodide Peroxidase	A hemeprotein that catalyzes the oxidation of the iodide radical to iodine with the subsequent iodination of many organic compounds, particularly proteins. EC 1.11.1.8.	Iodinase,Iodothyronine 5'-Deiodinase,Iodothyronine Deiodinase,Iodotyrosine Deiodase,Thyroid Peroxidase,Thyroxine 5'-Deiodinase,Thyroxine 5'-Monodeiodinase,5'-Deiodinase,Deiodinase,Iodotyrosine Deiodinase,Monodeiodinase,Reverse Triiodothyronine 5'-Deiodinase,T4-5'-Deiodinase,T4-Monodeiodinase,Tetraiodothyronine 5'-Deiodinase,Thyroxine Converting Enzyme,Triiodothyronine Deiodinase,5' Deiodinase,5'-Deiodinase, Iodothyronine,5'-Deiodinase, Reverse Triiodothyronine,5'-Deiodinase, Tetraiodothyronine,5'-Deiodinase, Thyroxine,5'-Monodeiodinase, Thyroxine,Deiodase, Iodotyrosine,Deiodinase, Iodothyronine,Deiodinase, Iodotyrosine,Deiodinase, Triiodothyronine,Enzyme, Thyroxine Converting,Iodothyronine 5' Deiodinase,Peroxidase, Iodide,Peroxidase, Thyroid,Reverse Triiodothyronine 5' Deiodinase,T4 5' Deiodinase,T4 Monodeiodinase,Tetraiodothyronine 5' Deiodinase,Thyroxine 5' Deiodinase,Thyroxine 5' Monodeiodinase,Triiodothyronine 5'-Deiodinase, Reverse
D007668	Kidney	Body organ that filters blood for the secretion of URINE and that regulates ion concentrations.	Kidneys
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008861	Microsomes	Artifactual vesicles formed from the endoplasmic reticulum when cells are disrupted. They are isolated by differential centrifugation and are composed of three structural features: rough vesicles, smooth vesicles, and ribosomes. Numerous enzyme activities are associated with the microsomal fraction. (Glick, Glossary of Biochemistry and Molecular Biology, 1990; from Rieger et al., Glossary of Genetics: Classical and Molecular, 5th ed)	Microsome
D011441	Propylthiouracil	A thiourea antithyroid agent. Propythiouracil inhibits the synthesis of thyroxine and inhibits the peripheral conversion of throxine to tri-iodothyronine. It is used in the treatment of hyperthyroidism. (From Martindale, The Extra Pharmacopeoia, 30th ed, p534)	6-Propyl-2-Thiouracil,6 Propyl 2 Thiouracil
D002001	Adipose Tissue, Brown	A thermogenic form of adipose tissue composed of BROWN ADIPOCYTES. It is found in newborns of many species including humans, and in hibernating mammals. Brown fat is richly vascularized, innervated, and densely packed with MITOCHONDRIA which can generate heat directly from the stored lipids.	Brown Fat,Hibernating Gland,Brown Adipose Tissue,Fat, Brown,Tissue, Brown Adipose
D004229	Dithiothreitol	A reagent commonly used in biochemical studies as a protective agent to prevent the oxidation of SH (thiol) groups and for reducing disulphides to dithiols.	Cleland Reagent,Cleland's Reagent,Sputolysin,Clelands Reagent,Reagent, Cleland,Reagent, Cleland's
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D013974	Thyroxine	The major hormone derived from the thyroid gland. Thyroxine is synthesized via the iodination of tyrosines (MONOIODOTYROSINE) and the coupling of iodotyrosines (DIIODOTYROSINE) in the THYROGLOBULIN. Thyroxine is released from thyroglobulin by proteolysis and secreted into the blood. Thyroxine is peripherally deiodinated to form TRIIODOTHYRONINE which exerts a broad spectrum of stimulatory effects on cell metabolism.	L-Thyroxine,Levothyroxine,T4 Thyroid Hormone,3,5,3',5'-Tetraiodothyronine,Berlthyrox,Dexnon,Eferox,Eltroxin,Eltroxine,Euthyrox,Eutirox,L-3,5,3',5'-Tetraiodothyronine,L-Thyrox,L-Thyroxin Henning,L-Thyroxin beta,L-Thyroxine Roche,Levo-T,Levothroid,Levothyroid,Levothyroxin Deladande,Levothyroxin Delalande,Levothyroxine Sodium,Levoxine,Levoxyl,Lévothyrox,Novothyral,Novothyrox,O-(4-Hydroxy-3,5-diiodophenyl) 3,5-diiodo-L-tyrosine,O-(4-Hydroxy-3,5-diiodophenyl)-3,5-diiodotyrosine,Oroxine,Sodium Levothyroxine,Synthroid,Synthrox,Thevier,Thyrax,Thyroxin,Tiroidine,Tiroxina Leo,Unithroid,L Thyrox,L Thyroxin Henning,L Thyroxin beta,L Thyroxine,L Thyroxine Roche,Levo T,Thyroid Hormone, T4
D014284	Triiodothyronine	A T3 thyroid hormone normally synthesized and secreted by the thyroid gland in much smaller quantities than thyroxine (T4). Most T3 is derived from peripheral monodeiodination of T4 at the 5' position of the outer ring of the iodothyronine nucleus. The hormone finally delivered and used by the tissues is mainly T3.	Liothyronine,T3 Thyroid Hormone,3,3',5-Triiodothyronine,Cytomel,Liothyronine Sodium,Thyroid Hormone, T3