title: Presence of thyroxine 5'-monodeiodinase activity in kidney homogenates of the frog, Rana ridibunda.
abstract: Conversion of thyroxine (T4) to triiodothyronine (T3), which was demonstrated in the 6000-g supernatant fraction of kidney homogenates prepared from Rana ridibunda frogs, was influenced by substrate (0.19-1.5 microM) and homogenate (39-625 mg kidney/ml) concentration and by temperature (19.5-36.5 degrees) and duration (1 hr vs 2 hr) of incubation. Heating destroyed 5'-monodeiodinase activity. Addition of dithiothreitol (DTT) to the reaction mixture appeared to be essential to quantitate T3 production, which even increased markedly in the copresence of ethylenediaminetetraacetate (EDTA). Sensitivity of the DDT + EDTA-stimulated enzyme to propylthiouracil inhibition (25-45%) was discussed in relation with the ambient thiol concentration.
authors.affiliation: Laboratory of Comparative Endocrinology, Catholic University of Leuven, Belgium.
authors.forename: G F
authors.initials: GF
authors.lastname: Jacobs
authors.forename: E R
authors.initials: ER
authors.lastname: Kühn
mesh_terms: D000818:Animals; D004229:Dithiothreitol / Q000494:pharmacology; D066298:In Vitro Techniques; D007453:Iodide Peroxidase / Q000032:analysis*; D007668:Kidney / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D011441:Propylthiouracil / Q000494:pharmacology; D011863:Radioimmunoassay; D011895:Rana ridibunda; D013696:Temperature; D013974:Thyroxine / Q000378:metabolism; D014284:Triiodothyronine / Q000096:biosynthesis
chemical_list: D014284:Triiodothyronine; D011441:Propylthiouracil; D007453:Iodide Peroxidase; D013974:Thyroxine; D004229:Dithiothreitol