Conversion of thyroxine into tri-iodothyronine by rat liver homogenate. 1975


By using a highly specific radioimmunoassay the formation of tri-iodothyronine by the deiodination of thyroxine was studied in rat liver homogenate. Several observations suggest that the reaction observed is enzymic in nature. Pre-heating the homogenate for 30 min at 56 degrees C completely abolished conversion of thyroxine into tri-iodothyronine; the component of rat liver homogenate responsible could be saturated with substrate; iodotyrosines displayed competitive activity. Between 0 degrees and 37 degrees C, the tri-iodothyronine-production rate was positively correlated with incubation temperature. The addition of NAD+ enhanced conversion into tri-iodothyronine, which suggests that an oxidative mechanism is involved. 5-Propyl-2-thiouracil and 6-propyl-2-thiouracil, both known to prevent deiodination in vivo, greatly decreased the deiodiantion activity of rat liver homogenate.

UI MeSH Term Description Entries
D007470 Monoiodotyrosine A product from the iodination of tyrosine. In the biosynthesis of thyroid hormones (THYROXINE and TRIIODOTHYRONINE), tyrosine is first iodized to monoiodotyrosine. Iodotyrosine
D008099 Liver A large lobed glandular organ in the abdomen of vertebrates that is responsible for detoxification, metabolism, synthesis and storage of various substances. Livers
D008297 Male Males
D009243 NAD A coenzyme composed of ribosylnicotinamide 5'-diphosphate coupled to adenosine 5'-phosphate by pyrophosphate linkage. It is found widely in nature and is involved in numerous enzymatic reactions in which it serves as an electron carrier by being alternately oxidized (NAD+) and reduced (NADH). (Dorland, 27th ed) Coenzyme I,DPN,Diphosphopyridine Nucleotide,Nadide,Nicotinamide-Adenine Dinucleotide,Dihydronicotinamide Adenine Dinucleotide,NADH,Adenine Dinucleotide, Dihydronicotinamide,Dinucleotide, Dihydronicotinamide Adenine,Dinucleotide, Nicotinamide-Adenine,Nicotinamide Adenine Dinucleotide,Nucleotide, Diphosphopyridine
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
D011863 Radioimmunoassay Classic quantitative assay for detection of antigen-antibody reactions using a radioactively labeled substance (radioligand) either directly or indirectly to measure the binding of the unlabeled substance to a specific antibody or other receptor system. Non-immunogenic substances (e.g., haptens) can be measured if coupled to larger carrier proteins (e.g., bovine gamma-globulin or human serum albumin) capable of inducing antibody formation. Radioimmunoassays
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
D013696 Temperature The property of objects that determines the direction of heat flow when they are placed in direct thermal contact. The temperature is the energy of microscopic motions (vibrational and translational) of the particles of atoms. Temperatures
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

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