The response of individual polypeptides of the mammalian respiratory chain to thyroid hormone.

The effects of thyroid hormone on the accumulation of inner membrane polypeptides in rat liver mitochondria have been investigated using Western blot analysis. Respiration and mitochondrial protein synthesis were also measured. Levels of the subunits of cytochrome oxidase, the cytochrome bc1 complex, and the beta-subunit of F1-ATPase increase relatively late, requiring 3-6 days of treatment and high doses of hormone. In contrast, respiration increases under conditions in which no significant accumulation of individual subunits is observed. Our results indicate that increased oxidative capacity of mitochondria can be divided into an early response which probably involves metabolic regulation of mitochondrial respiration by hormone and a later response which is due to elevated mitochondrial protein synthesis and the accumulation of polypeptides of the respiratory chain.