exposed, In the exposed, the isoleucine content of both chains is elevated but more so in the 8 than in the @ chain. : The markedly higher isoleucine content in the B chain of those exposed is consistent with the postulate that the gamma rays induced base substitution mutations in ervthropoietic stem cells. The small pre-< and pre-= peaks (Figure 2) contain polypeptides in which oxidation of methionine residues and limited deamidation of asparagine or glutamine residues have occurred, which cause a net increase in the negative charge on these molecules. The pre~ and pre-f regions are more prominent in samples that have been stored for longer periods of time, these samples were stored for 4 to 6 months between preparing the globin and performing the chain separations. The isoleucine content in the pre~2 and pre-> regions is higher than would be predicted on the basis of random substitution of isoleucine for other acids owing to single base changes and random of asparagine and glutamine. oxidation of methionine and deamidation The results suggest that molecules with amino acid substitutions are more susceptible to oxidation and deamidation. Considering the high probability that much of the increased isoleucine in the hemoglobin of the exposed Marshallese resulted from base substitution somatic mutations, an increase in isoleucine incorporation into hemoglobin per rad of exposure can be estimated (Figure 3), The dose required to double the normal substitution frequency of the controls is 100 to 105 R. Based on the data (Table 1 and Figure 3), the isoleucine substitution frequency increased by 0.0320 X 107 per amino acid residuc per R. However,