Evidence for induction by thyroid hormone of cytosolic proteins which control mitochondrial protein synthesis.

The effect of thyroid hormone on the generation of modulators of mitochondrial protein synthesis was investigated. The modulators were present in the 150,000 X g supernatant (S-150) prepared from Wistar rat liver and kidney. In young rats (50 g BW), a stimulator was found in liver, and an inhibitory modulator was present in kidney tissue. Generation of these modulators was stimulated by T4 administration to the animals. In aged rats (200 g BW), the production of an inhibitory modulator in both liver and kidney was stimulated by thyroid hormone administration. Both the stimulatory and inhibitory modulators were inactivated by pretreatment with trypsin. The mol wt of these modulators was estimated by gel filtration study, and for both the stimulatory and inhibitory modulator proteins was approximately 10,000. The results suggested that thyroid hormone regulates mitochondrial protein synthesis through the stimulation of synthesis of mitochondrial protein synthesis modulators and that the tissue-specific modulators (stimulatory in liver and inhibitory in kidney) can be produced in young animals. In aged animals, however, it is postulated that thyroid hormone stimulates biosynthesis of an inhibitory modulator in both liver and kidney.