The peculiarities of protein and RNA syntheses in the hepatic mitochondria of young and old animals: studies without the use of an antibiotic

Abstract Pulse-labelling in the presence of antibiotics is so widely used for studying mitochondriogenesis that the shortcomings of the method is usually overlooked. In this article, we present the results of experiments on the biogenesis of mitochondria done without the use of antibiotics. The method of Kitagawa and Sugimoto (1980) for the estimation of in vivo translational activity of rat liver mitochondria without the use of antibiotics was employed. The syntheses of RNA and protein in rat liver mitochondria of young and old animals was investigated. Incorporation of 14 C-ATP into the RNA of isolated mitochondria occurs at the same level in both young and old animals. However, the incorporation of 14 C-leucine into the two fractions of mitochondria, i.e. mitochondrial protein of nucleo-cytoplasmic origin and those of intrinsic mitochondrial origin are at the same level for young animals. In old animals, the incorporation of the tracer into mitochondrial protein of intrinsic mitochondrial origin (which is at the same level as that of young animals) is three times greater than the incorporation of the tracer into mitochondrial protein of nucleo-cytoplasmic origin. These findings suggest that the role of the mitochondrial genome in the biogenesis of mitochondria increases at senesence and that the synthesis of corresponding regulatory proteins which are of nucleo-cytoplasmic origin decreases at senesence.