The binding of urethan with DNA, RNA, nuclear proteins, and cytoplasmic proteins of rat organs was examined with ethyl carbamate-1-14C, ethyl carbamate-2-3H, and ethyl carbamate carboxyl-14C. A definite radioactivity in nucleic acids and proteins was found after administration of ethyl carbamate-1-14C and ethyl carbamate-2-3H, while negligible activity was found after administration of ethyl carbamate carboxyl-14C. The study of the labeled compounds formed between urethan and DNA or RNA, in the case of ethyl carbamate-1-14C, demonstrated that the activity was present as a result of a true interaction and not because of metabolic utilization. All the nucleotides that resulted from alkaline or enzymatic hydrolysis of DNA and RNA were labeled. In the case of RNA, most of the activity of AMP, GMP, and CMP was removed from the bases with acid hydrolysis, and it presented a characteristic behavior on paper chromatography. In the case of DNA, the activity remained bound to the bases after the same hydrolysis.

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This work was supported by a grant from Consiglio Nazionale delle Ricerche, Rome, Italy.

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