Methylene blue photosensitised strand cleavage of DNA: effects of dye binding and oxygen.
It is shown that methylene blue (MB+) photosensitises DNA in either aerated or deaerated solutions, causing direct cleavage of phosphodiester bonds and rendering additional bonds labile to alkali. Evidence from unwinding and fluorimetric studies indicates that MB+ binds to DNA in at least 2 ways. Intercalation, which optimally induces helical unwinding of 24 degrees +/- 2 degrees per MB+, is markedly reduced upon neutralisation by Mg2+ of the DNA phosphates, while significant non-intercalative binding persists as shown by substantial fluorescence quenching at Mg2+ concentrations where there is little unwinding. MB+ induces photolysis at both low and high Mg2+ concentration - intercalation is apparently not required for photolysis. The quantum yield for strand breakage varies from 1-3 X 10(-7) under different conditions and is oxygen enhanced. The DNA cleavage is guanine specific. The 3' termini of the primary MB+-induced DNA photoproducts, unlike those generated by chemical sequencing retain an alkali labile adduct on the terminal phosphate.
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Department of Genetics, University of Dublin, Trinity College, Ireland.
McConnell
D J
DJ
Kelly
J M
JM
van der Putten
W J
WJ
D004247:DNA / Q000187:drug effects* / Q000528:radiation effects; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004278:DNA, Superhelical / Q000187:drug effects; D006147:Guanine / Q000528:radiation effects; D006868:Hydrolysis; D007364:Intercalating Agents / Q000494:pharmacology*; D008274:Magnesium / Q000378:metabolism; D008751:Methylene Blue / Q000494:pharmacology*; D009690:Nucleic Acid Conformation / Q000187:drug effects; D009994:Osmolar Concentration; D010100:Oxygen / Q000378:metabolism; D010777:Photochemistry; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D026082:Singlet Oxygen
D004278:DNA, Superhelical; D007364:Intercalating Agents; D011838:Radiation-Sensitizing Agents; D026082:Singlet Oxygen; D006147:Guanine; D004247:DNA; D004264:DNA Topoisomerases, Type I; D008274:Magnesium; D010100:Oxygen; D008751:Methylene Blue