Effect of Inhibition of Mitochondrial Protein Synthesisin VitroUpon Thyroxine Stimulation of Oxygen Consumption

It has been suggested that the calorigenic activity of thyroid hormones is secondary to their ability to stimulate mitochondrial or ribosomal protein synthesis. Since thyroid hormones stimulate both protein synthesis and oxgyen consumption in mitochondiia from normal rats, the effect of inhibition of protein synthesis upon thyroxine (T4) stimulation of mitochondrial oxygen consumption in vitro was examined. T4 (50 JUM) stimulated leucine incorporation 125% and oxygen consumption 100% (without ADP) in mitochondria from normal rats in vitro. The effects were linear over 8 min. Chloramphenicol (250 /xM) or puromycin (100 fjM) inhibited leucine incorporation 85–91% in control and T4-containing reactions without affecting oxygen consumption in either. ADP/O and respiratory control ratios were significantly depressed by T4; however, the antibiotics had no effects on these values, with or without T4. In addition, T4 was found not to alter the rate of decay of mitochondrial protein, newly formed in vitro. (Endocrinology89: 534, 1971)