Biomaterial Database

In-vitro conversion of thyroxine to tri-iodothyronine by chicken hepatic 5'-deiodinase: kinetic studies. 1986

S K Lam, and S Harvey

In-vitro studies with chicken liver homogenates demonstrate that the conversion of thyroxine (T4) to tri-iodothyronine (T3) is dependent upon tissue concentration, time of incubation, pH, temperature, the presence of dithiothreitol (DTT) and the concentration of substrate (T4), and is heat-labile. The generation of T3 is inhibited by iopanoic acid and 6-n-propyl-2-thiouracil. The kinetics of conversion of T4 to T3, determined by Lineweaver-Burke analysis, indicated an apparent Michaelis-Menten constant (Km) of 1.16 mumol/l with a maximum velocity (Vmax) of 44.57 pmol T3 generated/mg protein per min from T4. Dithiothreitol appears to behave as a co-substrate for this system with an apparent Km of 98.5 mumol/l and a Vmax of 1.41 pmol T3 generated/mg protein per min at a T4 concentration of 5 mumol/l. These data suggest that the conversion of T4 to T3 in fowl proceeds by means of an enzymatic system, probably 5'-monodeiodinase, and is responsible for maintaining T3 levels in vivo.

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
D007700	Kinetics	The rate dynamics in chemical or physical systems.
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
D002645	Chickens	Common name for the species Gallus gallus, the domestic fowl, in the family Phasianidae, order GALLIFORMES. It is descended from the red jungle fowl of SOUTHEAST ASIA.	Gallus gallus,Gallus domesticus,Gallus gallus domesticus,Chicken
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
D006863	Hydrogen-Ion Concentration	The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH	pH,Concentration, Hydrogen-Ion,Concentrations, Hydrogen-Ion,Hydrogen Ion Concentration,Hydrogen-Ion Concentrations
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