Chemical carcinogenesis. I. Rat liver tRNA ethylation by ethionine

The mechanism of biological action of the powerful carcinogen ethionine is still unknown at the present. Here the "in vivo" tRNA ethylation after administration of radioactive ethionine to rats has been reinvestigated. In particular, the radioactive "pyrimidine nucleotides" fraction was examined: chromatographic and ultraviolet-spectral analyses indicated the presence of imidazole-ring-opened derivatives of guanosine in this fraction, the identification of which is reported in the accompanying paper. These data appear particularly interesting especially when considering the recently advanced hypothesis (6,7) of a transversion purine----pyrimidine as the initial precancerous biochemical lesion in chemical carcinogenesis.