The interaction between hydrogen peroxide and the DNA-Cu(I) complex: effects of pH and buffers.
The rate of interaction between H2O2 and the DNA-Cu(I) complex increases with pH and with salt (NaCl) concentration, suggesting that HO2- is involved. The pH dependence can be fitted, assuming k(DNA-Cu(I) + H2O2) = 1 M-1 S-1 and k(DNA-Cu(I) + HO2-) = 10(5) M-1 S-1 (at low salt concentrations). These interactions cause DNA damage, probably due to the formation of .OH radicals near the site of Cu(I) fixation at DNA bases. About 70% of the intermediates DNA.OH, formed by free .OH radicals were found capable of reducing Cu(II) to regenerate DNA-Cu(I); thus a (limited) reaction chain involving "reductive propagation" by DNA.OH species appears feasible upon reaction of H2O2 with DNA-Cu(I). .OH-induced intermediates of poly(C) are more efficient (about 80%), those of poly(A) and poly(G) are less efficient (about 38%), in reducing Cu(II). Certain organic buffers, particularly HEPES and PIPES, promote autoxidation in DNA/Cu(II)/H2O2 systems, and it is shown that .OH-induced buffer intermediates as well as secondary stable buffer products can engage in "reductive propagation" of redox cycles.
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WA
Universität Freiburg, Institut für Biophysik und Strahlenbiologie, Bundesrepublik Deutschland.
D002021:Buffers; D003300:Copper; D003574:Cytochrome c Group / Q000378:metabolism; D004247:DNA / Q000737:chemistry*; D005609:Free Radicals; D006861:Hydrogen Peroxide; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D013056:Spectrophotometry, Ultraviolet
D002021:Buffers; D003574:Cytochrome c Group; D005609:Free Radicals; D003300:Copper; D004247:DNA; D006861:Hydrogen Peroxide