title: Inactivation and affinity-labeling of rat liver iodothyronine deiodinase with N-bromoacetyl-3,3',5-triiodothyronine.
abstract: The thyroid hormone derivative N-bromoacetyl-3,3',5-triiodothyronine (BrAcT3) acts as an active site-directed inhibitor of rat liver iodothyronine deiodinase. Lineweaver Burk analysis of enzyme kinetic measurements showed that BrAcT3 is a competitive inhibitor of the 5'-deiodination of 3,3',5'-triiodothyronine (rT3) with an apparent Ki value of 0.1 nM. Preincubations of enzyme with BrAcT3 indicated that inhibition by this compound is irreversible. The inactivation rate obeyed saturation kinetics with a limiting inactivation rate constant of 0.35 min-1. Substrates and substrate analogs protected against inactivation by BrAcT3. Covalent incorporation of 125I-labeled BrAcT3 into "substrate-protectable" sites was proportional to the loss of deiodinase activity. The results suggest that BrAcT3 is a very useful affinity label for rat liver iodothyronine deiodinase.
mesh_terms: D000345:Affinity Labels / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D007453:Iodide Peroxidase / Q000037:antagonists & inhibitors*; D007700:Kinetics; D008862:Microsomes, Liver / Q000201:enzymology*; D010544:Peroxidases / Q000037:antagonists & inhibitors*; D051381:Rats; D013379:Substrate Specificity; D013963:Thyroid Hormones / Q000494:pharmacology; D014284:Triiodothyronine / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D000345:Affinity Labels; D013963:Thyroid Hormones; D014284:Triiodothyronine; C036219:N-bromoacetyl-3,3',5-triiodothyronine; D010544:Peroxidases; D007453:Iodide Peroxidase