[Synthesis of mtDNA and proteins coded by mtDNA in liver mitochondrial fractions of rats of varying age].

The in vivo synthesis of mtDNA and mtDNA-coded proteins was studied in the whole population and in separate fractions (heavy, middle and light) of liver mitochondria from young (3-4 months), adult (6-8 months) and old (24-26 months) rats. The synthesis rate was estimated from the value of relative specific radioactivity which represented a ratio of specific radioactivity of acid insoluble fraction to that of acid soluble fraction in suspension aliquot of isolated mitochondria. It was found that the synthesis rate of mtDNA in the whole mitochondrial population was increased in the adult rats and decreased in the old animals. The same direction of changes was noticed in heavy and light mitochondrial fractions. Moreover, at any age the synthesis rate of mtDNA was higher in light fractions as compared to other fractions. In the whole mitochondrial population, the synthesis rate of proteins coded by mtDNA was also increased in adult rats and decreased in old animals. However, this decrease was less expressed than in mtDNA case. The increase in the synthesis rate of mitochondrial proteins was noted in all mitochondrial fractions too, whereas its decrease in the old age was marked in the light mitochondria only. Owing to the above peculiarities of age-related changes of the synthesis rate of mtDNA and proteins coded by mtDNA, there takes place the prevalence with age of protein synthesis over mtDNA synthesis in the whole population and in the fractions of rat liver mitochondria.