Spécificité des hormones thyroïdiennes et de l'hormone de croissance sur les propriétés et la protéinogenèse des particules subcellulaires: I. Rats thyroïdectomisés

Summary Protein biosynthesis is controlled by growth hormone (GH) and iodothyronines, moreover the latter regulate metabolic activity. Growth hormone had little incidence on oxidative phosphorylation. Respiratory control index (RC) and P/O ratios with various respiratory substrates were about the same with liver mitochondria isolated from thyroidectomized animals treated or not with GH. Respiration of thyroidectomized rat liver mitochondria with succinate or β-hydroxybutyrate was lowered in the controlled state, but whereas the P/O ratios were about the same for normal and operated animals, the respiratory control index was increased with β-hydroxybutyrate in hypothyroid rats. It appears that the thyroid hormones affected the three phosphorylation sites differently. Thyroidectomy decreased the biological decay of L-leucine (U- 14 C). By a double isotope procedure the ratio of 3 H- and 14 C-leucine was strongly suggestive of a slower protein turnover rate of whole mitochondria and especially inner mitochondrial membrane; differences were much less significant with other subcellular hepatic fractions (nuclei, microsomes, outer mitochondrial membrane and cell sap). These results suggest an action of thyroid hormones on the mitochondrial genome which controls the biosynthesis of some proteins of the inner mitochondrial membrane. The uncoupling effect of iodothyronines may be considered as physiologic and seems linked to the turnover rate of some protein components of the inner mitochondrial membrane.