| Thyroid hormones act at two levels in mitochondria. It has been shown that in rats T3 stimulates the synthesis of UCP2 and UCP3, which can uncouple the proton gradient. Additionally, T2 binds to complex IV on the matrix side, inducing slip in cytochrome c oxidase. The term slip means that complex IV pumps fewer protons per electron transported through the complex, resulting in thermogenesis. The action of T3 could explain, in part, the long-term and T2 the short-term thermogenic effects of thyroid hormones.
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