Hoechst 33258 photosensitization of 5-iododeoxyuridine-substituted DNA to 365 nm light: dependence of dehalogenation on the dye-to-nucleotide ratio.
DNA containing 5-iododeoxyuridine substituted at levels ranging from 1 to 24% was irradiated at 365 nm in the presence of various amounts of the Hoechst dye 33258. The subsequent loss of iodine was measured by following the loss of radioactive iodine (125I) from filter immobilized DNA subjected to repeated washings. A plot of the photochemical cross section (sigma B) for this process as a function of r, the molar ratio of dye added per nucleotide present, shows a maximum at r = 0.04 to 0.06, followed by a decrease with increasing dye-to-phosphate ratios to give a minimum at r = 0.5. Increasing the amounts of dye further results in sigma B reaching a second maximum at r greater than or equal to 1, after which it levels off. An attempt was made to interpret these results in terms of the binding models currently employed for analyzing binding of Hoechst dye to DNA. Chain breaks as measured in alkali were also measured and found to be enhanced by the dye; the ratio of breaks per iodine loss was 0.9.
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School of Public Health, University of Alabama, Birmingham 35294.
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D006690:Bisbenzimidazole / Q000494:pharmacology; D004269:DNA, Bacterial / Q000737:chemistry / Q000187:drug effects / Q000528:radiation effects*; D007065:Idoxuridine; D010777:Photochemistry; D014466:Ultraviolet Rays
D004269:DNA, Bacterial; D007065:Idoxuridine; D006690:Bisbenzimidazole