Liver ribosomes from rats pretreated with carcinogenic agents release a ferritin fraction which differs from that of normal ribosomes. This was demonstrated by disc-electrophoresis of the native protein and of the subunits produced by LiCl-urea-treatment. Moreover, the nucleoproteids into which those ribosomes dissociate during incubation with protease-free ribonuclease show a significant alteration in their electrophoretic pattern. - The Michaelis - constant of ribonuclease was found about

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... redfold higher, which indicates that the superficial RNA structures are masked by the pathological ferritin to a greater extent than the RNA of normal ribosomes.