The binding of ethyl carbamate to DNA of mouse liver in vivo: The nature of the bound molecule and the site of binding

Ethyl carbamate, labelled at C₁ with ¹⁴C, bound in vivo to liver DNA of intact and partially hepatectomised mice. Isotope (¹⁸O) enrichment was not detected in the oxygen of liver DNA of mice injected with [¹⁸O] ethyl carbamate, C₂H₅-¹⁸O-CO-NH₂. This suggests that it was the ethyl group and not the ethoxy group which bound to DNA. Chromatographic analysis of acid hydrolysates of liver DNA from mice treated with [1-¹⁴C] ethyl carbamate provided no evidence of alkylation or other form of binding to purine or pyrimidine bases. On relatively mild acid hydrolysis the alkyl group remained bound to the "apurinic acid" fraction, while more vigorous hydrolysis lead progressively first to its separation as highly ionisable hydrophilic non-volatile compounds and then to its loss as a volatile compound. DNAase I followed by phosphodiesterase hydrolysis also split off the ¹⁴C-containing group as a volatile compound. The volatile compound was identified as ethanol. These results suggest that the alkyl group was bound as an ester to a phosphate group in the DNA chain. Results with DNA from partially hepatectomised mice did not differ from those with DNA from intact mice.