Inhibition by Actinomycin D of Oxidation-dependent Biosynthesis in Sarcoma 37 Ascites Cells

When Sarcoma 37 ascites cells were incubated in the presence of actinomycin D, protein synthesis was inhibited. The inhibitory effect could be prevented or relieved by glucose or by a variety of glycolyzable substrates. The inhibitory effect was independent of the concentration of the labeled amino acid precursor. Under conditions inhibitory to protein synthesis, no significant inhibition of respiration or of amino acid uptake was observed. Actinomycin D inhibited amino acid incorporation into ribosomal and soluble protein, as well as into soluble ribonucleic acid, and these inhibitory effects were all abolished by the presence of glucose. Three analogues of actinomycin D, which were inactive as inhibitors of RNA synthesis, were inactive as inhibitors of protein synthesis in the present studies. Actinomycin D also inhibited the incorporation of mevalonic acid into sterols, and the inhibition was relieved by glucose. Although the characteristics of these inhibitions suggested an interference with the availability of oxidative energy, measurements of levels of adenine nucleotides and of incorporation of 32P-labeled orthophosphate into ATP failed to show an effect of the antibiotic on oxidative phosphorylation.