title: Induction by 3, 5, 3' L-triiodothyronine of L-ornithine decarboxylase in rat heart muscle.
abstract: Injection of 3,5,3' L-triiodothyronine (15 micrograms/100 g) induces a biphasic enhancement of rat heart ornithine decarboxylase (EC. 4.1.17) activity after 4 and 21 hours. This induction is observed after each daily injection, but to a lesser extent. The properties of partially purified basal enzyme and induced enzyme, at 21h, after single injections have been compared. 1) Affinity for ornithine is the same for both enzymes, but affinity for pyridoxal-phosphate is 40-fold higher for the induced one. 2) Thermostability studies suggest that basal and induced enzymes have different conformations. 3) The two enzymes have similar immuno-reactivity. 4) The comparisons of the time-dependent activity curve after injection and of the antigen/activity ratio suggests that triiodothyronine induces the synthesis of new molecules of enzymes and that an inhibition of the enzyme activity also occurs which explains the biphasic induction.
mesh_terms: D000818:Animals; D002262:Carboxy-Lyases / Q000096:biosynthesis*; D004790:Enzyme Induction; D006321:Heart / Q000187:drug effects; D006358:Hot Temperature; D008297:Male; D009206:Myocardium / Q000201:enzymology*; D009952:Ornithine / Q000378:metabolism; D009955:Ornithine Decarboxylase / Q000096:biosynthesis*; D011732:Pyridoxal Phosphate / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D014284:Triiodothyronine / Q000494:pharmacology*
chemical_list: D014284:Triiodothyronine; D011732:Pyridoxal Phosphate; D009952:Ornithine; D002262:Carboxy-Lyases; D009955:Ornithine Decarboxylase