Protein synthesis in adrenal mitochondrial and post-mitochondrial fractions of ACTH-treated rats

Short and prolonged administration of ACTH was used to study the effects of the hormone on protein synthesis in two subcellular fractions obtained from rat adrenals incubated in the presence of a (14C)-labelled amino acid mixture. Acute treatment with ACTH produced an increased labelling of the proteins of the post-mitochondrial (POST-MIT) fraction only. On the other hand, treatment with ACTH for 4-28 days, significantly increased the specific activity of proteins in the mitochondrial (MIT) fraction, without change in the radiolabelling of the POST-MIT fraction. The incorporation of (14C)-labelled amino acids into the proteins of the MIT and POST-MIT fractions, from control or ACTH-treated adrenals, was reduced by inhibitors of cytoplasmic protein synthesis (puromycin and cycloheximide). This suggests that the increased labelling of the MIT fraction after prolonged ACTH might be related to a translocation of cytoplasmic proteins to the mitochondrion.