THE TRANSLATION SYSTEM OF RAT-HEART MUSCLE MITOCHONDRIA IS STIMULATED FOLLOWING TREATMENT WITH L-TRIIODOTHYRONINE

In vitro translation of mitochondrial translation products by mitochondria isolated from the myocardia of rats injected with L-triiodothyronine [T3] daily for 5 days was compared with those ot euthyroid animals. The incorporation of 35S-methionine into proteins was greater by heart mitochondria isolated from T3-treated rats than by those isolated from euthyroid animals. This increase is due to a stimulation of mitochondrial protein synthesis rather than being the result of a reduction in the rate of protein degradation or an increase in the specific radioactivity of the amino acid pool. The polypeptide profile of mitochondrial translation products is the same in heart mitochondria isolated from euthyroid and T3-treated animals. The relative increase in the rates of synthesis of mitochondrial translation products is non-uniform. The hormone acts by inducing a general but non-uniform increase in the activity of the mitochondrial transcription and/or translation system(s).