Moreno M, Berry M J, Horst C, Thoma R, Goglia F, Harney J W, Larsen P R, Visser T J
Department of Internal Medicine III, Erasmus University Medical School, Rotterdam, The Netherlands.
FEBS Lett. 1994 May 16;344(2-3):143-6. doi: 10.1016/0014-5793(94)00365-3.
The prohormone thyroxine (T4) is activated by outer ring deiodination (ORD) to 3,3',5-triiodothyronine (T3) and both hormones are degraded by inner ring deiodination (IRD) to 3,3',5'-triiodothyronine (rT3) and 3,3'-diiodothyronine, respectively. Indirect evidence suggests that the type I iodothyronine deiodinase (ID-I) in liver has both ORD and IRD activities, with preference for rT3 and sulfated iodothyronines as substrates. To establish this, we have compared the ORD of rT3 and IRD of T3 and T3 sulfate by homogenates of cells transfected with rat ID-I cDNA and by rat liver microsomes. In both preparations rT3 is the preferred substrate, while deiodination of T3 is markedly accelerated by its sulfation. Kinetic analysis provided similar Km and Vmax values in cell homogenates and liver microsomes. These data demonstrate unequivocally that ID-I is capable of both activating and inactivating thyroid hormone by ORD and IRD, respectively.
前激素甲状腺素（T4）通过外环脱碘（ORD）被激活为3,3',5-三碘甲状腺原氨酸（T3），这两种激素分别通过内环脱碘（IRD）降解为3,3',5'-三碘甲状腺原氨酸（rT3）和3,3'-二碘甲状腺原氨酸。间接证据表明，肝脏中的I型碘甲状腺原氨酸脱碘酶（ID-I）同时具有ORD和IRD活性，优先以rT3和硫酸化碘甲状腺原氨酸为底物。为了证实这一点，我们比较了用大鼠ID-I cDNA转染的细胞匀浆以及大鼠肝脏微粒体对rT3的ORD和对T3及硫酸化T3的IRD。在这两种制剂中，rT3都是首选底物，而T3的硫酸化会显著加速其脱碘。动力学分析在细胞匀浆和肝脏微粒体中提供了相似的Km和Vmax值。这些数据明确表明，ID-I能够分别通过ORD激活甲状腺激素以及通过IRD使其失活。
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