Estimation of the In Vivo Translational Activity of Rat Liver Mitochondria without Use of an Antibiotic1

In order to estimate the in vivo translational activity of mitochondria without using cyclohex-imide, we developed a selective separation procedure for the mitochondrial translation products. The effects of cycloheximide and isotopic dilution kinetics on the precursor leucine pool indi-cate that the pH11.5 insoluble mitochondrial fraction is greatly enriched in mitochondrial translation products. The biogenesis of mitochondria is a cooperative process directed by two separate genetic systems, one in the nucleus, and the other in the mito-chondrion itself. Although the mitochondrial translation products account for only 5-15 % of total mitochondrial protein (1-3), these products are indispensable for the assembly of functional mitochondria (4). The lack of good methods for studying the translation activity of mitochondria has hindered the study of how mitochondrial translation interacts with that of the cytoplasm (5). Although the in vitro method with isolated mitochondria is useful for the identification of proteins coded by mitochondrial DNA (6, 7), regulation of the mitochondrial translation activity under various physiological conditions can not be investigated by this method. Labelling mito-chondrial proteins in vivo in the presence of cyclo-heximide (1, 8-11) may be a better approach to answer this question but the coordination wit