On the Electron Spin Resonances in DNA

Iron impurities are shown to account for characteristic electron spin resonances observed in samples of DNA. Comparative e.s.r. measurements on lyophilized samples were done in conjunction with static susceptibility measurements, trace analyses, and molecular degradation experiments to establish this correlation. It has not been possible to extract this iron by treatment with a chelating agent. Such resonances were in part accounted for by ferromagnetic iron contamination during extraction and handling. By modifying the method of Kay, Simmons, and Dounce to eliminate or minimize metal contamination—ionic and ferromagnetic—from sources both internal and external to the tissues used, it was possible to prepare iron-free (< 0.0004 per cent Fe), e.s.r.-free (< 0.001 per cent Fe) DNA. The samples showed 20 per cent protein (determined by the indole method), had a molecular weight 4 × 10 6 and were undenatured according to the density gradient experiment.