3,5-Diiodothyronine binds to subunit Va of cytochrome-c oxidase and abolishes the allosteric inhibition of respiration by ATP.

The short-term effects of thyroid hormones, which do not occur via gene expression, were postulated to be based on interaction of diiodothyronines with mitochondria. We demonstrate specific binding of labelled 3,5-diiodothyronine to subunit Va of cytochrome-c oxidase from bovine heart. 3,5-Diiodothyronine, and to a small extent triiodothyronine, but not thyroxine and thyronine, abolish the allosteric inhibition of ascorbate respiration of reconstituted cytochrome c oxidase by ATP [Arnold, S. & Kadenbach, B. (1997) Eur. J. Biochem. 249, 350-354]. This abolition of ATP-inhibition by 3,5-diiodothyronine is completely prevented by a monoclonal antibody to subunit Va. The results explain at the molecular level the short-term action of thyroid hormones on basal metabolic rate.