Evidence for a single enzyme in rat liver catalysing the deiodination of the tyrosyl and the phenolic ring of iodothyronines.
The enzymic 5'-deiodination of 3',5'-di-iodothyronine and 5-deiodination of 3,3',5-tri-iodothyronine by rat liver microsomal fractions were found to be characterized by apparent Km values of 0.77 and 17.4 microM respectively, 3',5'-Di-iodothyronine was a competitive inhibitor of 3,3',5-tri-iodothyronine 5-deiodination (Ki 0.65 microM) and 3,3',5-tri-iodothyronine was a competitive inhibitor of 3',5'-di-iodothyronine 5'-deiodination (Ki 19.6 microM). In addition, several radiographic contrast agents and iodothyronine analogues inhibited both reactions competitively and with equal potencies (r = 0.999). These results strongly suggest the existence of a single hepatic deiodinase acting on both the tyrosyl and phenolic ring of iodothyronines.
D000818:Animals; D003287:Contrast Media / Q000494:pharmacology; D004104:Diiodothyronines / Q000378:metabolism*; D066298:In Vitro Techniques; D007455:Iodine / Q000378:metabolism; D007700:Kinetics; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D051381:Rats; D013970:Thyronines / Q000378:metabolism*; D014284:Triiodothyronine / Q000378:metabolism*; D014441:Tyropanoate / Q000494:pharmacology
D003287:Contrast Media; D004104:Diiodothyronines; D013970:Thyronines; D014284:Triiodothyronine; D014441:Tyropanoate; C030102:3',5'-diiodothyronine; D007455:Iodine