Molecular dosimetry studies were carried out to measure the extent of binding of radio-labeled ethyl groups to the
DNA of Escherichia coli, V79 Chinese hamster cells and L5178Y mouse
lymphoma cells treated with
ethyl methanesulfonate (EMS). The results show that (1) the amount of ethylation of the
DNA is similar in these cells when treatment conditions are identical, (2) the relationship between dose to
DNA (ethylations per
nucleotide) versus exposure (mM applied concentration) is non-linear in the sense that less alkylation of the
DNA is observed at the higher exposures than would be predicted on the basis of proportionality between dose to
DNA and exposure, and (3) the non-linearity of the genetic response in the bacterial cells is not reflected in a non-linearity of the alkylation of the
DNA in those cells. Quantitative comparison of the frequencies of gene mutations in the various systems shows that the mutation frequency per unit of
DNA alkylation is heterogeneous among the mammalian cell systems and that the frequencies observed in the bacterial cells fall within the range observed with mammalian cells. Alkylation of the
DNA in the bone marrow, testis and liver of Swiss random-bred mice was also measured. The results support the conclusion that the distribution of the compound to the various tissues is rapid and probably uniform. Quantitative assessment of the cytological data (micronuclei, sister-chromatid exchanges, etc.) on the basis of dose was not as useful because of the low efficiency of EMS for inducing cytologically observable damage.