Macromolecular Synthesis in Hepatocyte Mitochondria of Aging Mice as Revealed by Electron Microscopic Radioautography II : Protein Synthesis

The aging changes of intramitochondrial protein synthesis in hepatocytes of several groups of litter mate mice at various ages, from fetal day 19, to postnatal newborn, adult month 1, 6, year 1 and 2, by means of electron microscopic radioautography after the injections with H-leucine were studied. From the results, it was found that some of the mitochondria in the hepatocytes were labeled with silver grains showing protein syntheses. Quantitative analysis revealed that the intramitochondrial labeling indices with silver grains increased from prenatal day to postnatal newborn, adult month 1, reaching the maxima, then decreased to senile year 1 to 2, indicating the aging changes. Based upon our findings, available literature on macromolecular synthesis in mitochondria of various cells such as proteins and nucleic acids, both DNA and RNA, are reviewed.