Regulation of protein synthesis in isolated mitochondria from regenerating rat liver

Possible sites in the mitochondrial protein synthetic/degradative scheme that might be responsible for the increased incorporation of [3H]leucine into protein by mitochondria isolated from regenerating liver over the levels found for mitochondria isolated from sham-operated controls were examined. The rate of degradation of newly synthesized protein in mitochondrial preparations from regenerating liver was not decreased but proceeded approximately 30% greater than that found for the sham-operated controls. The increased incorporation of [3H]leucine into protein could also not be accounted for by a stimulation in the extent of formation of leucyl-tRNALeu. In another experiment, isolated mitochondria were incubated with [3H]leucine and the input of mitochondrial ribosomes from regenerating liver and sham-operated controls equalized for analysis on sucrose density gradients. The 55-S ribosomes from regenerating liver mitochondria contained 2.7-fold greater radioactivity in their nascent polypeptide chains than those from control mitochondria. These results indicate that the stimulation in amino acid incorporation into protein due to liver regeneration is the direct result of enhanced polypeptide bond formation on mitochondrial ribosome-messenger RNA complexes.