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.
Evidence for a single enzyme in rat liver catalysing the deiodination of the tyrosyl and the phenolic ring of iodothyronines
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D Fekkes, G Hennemann, T J Visser; Evidence for a single enzyme in rat liver catalysing the deiodination of the tyrosyl and the phenolic ring of iodothyronines. Biochem J 1 March 1982; 201 (3): 673–676. doi: https://doi.org/10.1042/bj2010673
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