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. Author manuscript; available in PMC: 2020 Jul 1.
Published in final edited form as: J Endocrinol. 2019 Jul 1;242(1):T145–T160. doi: 10.1530/JOE-18-0704

Figure 2.

Figure 2.

Basic deiodinase reactions regulating thyroid hormone metabolism. The reactions catalyzed by the deiodinases remove iodine moieties from the phenolic (outer rings) or tyrosil (inner rings) rings of the iodothyronines. These pathways can activate T4 by transforming it into T3 via D1 or D2 or prevent it from being activated by converting it to the metabolically inactive form, reverse T3 (rT3) via D1 or D3. T2 is an inactive product common to deiodination of both T3 and rT3 and is rapidly metabolized by further deiodination (Bianco and Kim 2006 and van der Spek et al., 2017).