title: Adrenal gland 5'deiodinase activity (AG-5'd). Kinetic characterization and fractional turnover rate (FTr).
abstract: We determined the kinetic parameters as well as the fractional turnover rate (FTr) and half-life (t(1/2)) of rat adrenal gland 5'deiodinase activity (AG-5'D). Adrenal glands from male euthyroid or surgically thyroidectomized (Tx) Wistar rats were homogenized (HEPES, 10MM: ; pH 7.5; sucrose, 0.25M: ; EDTA 1MM: ) and centrifuged at 10,000g for 15 min at 4°C. The resulting crude microsomal supernatants were used for ail measurements of 5'D activity. Using rT(3) (2-500NM: ) the true Km and the Vmax values were of 20.2NM: and 289 fmol of I(-) release/mg protein/h. With T(4) as substrate these values were 5.8NM: and 622 fmol/h/mg protein. Protein inhibitor (cycloheximide 6 mg/100 g wt) administration allowed to determine an FTr of 0.68 h(-1) and a t(1/2) of 1.01 h. Results demonstrate that the greatest 5'D activity in the rat adrenal gland corresponds to isotype II, because the reaction is GTG and PTU-resistant (70-80%), accepts T(4) as a far better substrate than rT(3) (17-fold) and the former thyronine has a 50-90% inhibitory concentration in the 4-100NM: range. Furthermore, rats thyroidectomized for 5 and 15 days showed a conspicuous increase in cerebral cortex and adrenal 5'D-II activity. These characteristics as well as the rapid FTr and short †(1/2) are shared by type II 5'D present in rat pineal, pituitary and brain.
authors.affiliation: Centro de Neurobiología, Universidad Nacional Autónoma de México, Apartado Postal 70-228, 04510, D F, México.
authors.forename: M
authors.initials: M
authors.lastname: Luna
authors.forename: B
authors.initials: B
authors.lastname: Anguiano
authors.forename: C
authors.initials: C
authors.lastname: Valverde-R