title: Comparison of type I 5'-deiodination of thyroxine and of reverse-triiodothyronine in rat and chicken liver homogenates.
abstract: The characteristics of 5'-deiodination in the chicken liver have been compared to those in the rat. Using 6-n-propyl-2-thiouracil (PTU) at 1 mM in vitro, it was shown that, in accordance with former in vivo studies, only type I 5'-deiodinase exists in the liver of the chicken. When PTU was used in a concentration (10 microM) close to its Ki species differences could be demonstrated as for PTU sensitivity. 5'-Deiodinase in the chicken liver was more susceptible against the inhibitor. The early thiol-independent phase of deiodination was longer in the chicken than in the rat. Reverse-triiodothyronine (r-T3) seemed to be a more suitable substrate for this enzyme in the chicken when compared to either T4 degradation or r-T3 degradation in the rat. It is concluded that major characteristics of 5'-deiodination in the chicken are similar to those in the rat; however, the slight variances observed might explain some species differences found earlier.
mesh_terms: D000818:Animals; D002645:Chickens; D004229:Dithiothreitol / Q000494:pharmacology; D007453:Iodide Peroxidase / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D013045:Species Specificity; D013379:Substrate Specificity; D013974:Thyroxine / Q000378:metabolism*; D014285:Triiodothyronine, Reverse / Q000378:metabolism*
chemical_list: D014285:Triiodothyronine, Reverse; D007453:Iodide Peroxidase; D013974:Thyroxine; D004229:Dithiothreitol