Repair of oxidative guanine damage in plasmid DNA by indoles involves proton transfer between complementary bases.
We have used the single electron oxidizing agent (SCN)(2)(*)(-) (generated by gamma-irradiation of aqueous thiocyanate) to produce guanyl radicals in plasmid DNA. The stable product(s) formed from these radicals can be detected after conversion with a base excision repair endonuclease to single strand breaks. The yield of enzyme-induced breaks is decreased by the presence during irradiation of indole compounds. Rate constants for the reduction of DNA guanyl radicals by these indoles can be calculated from the concentration dependence of the attenuation in the yield of enzyme sensitive sites. Indoles bearing electron-donating groups (methoxy or methyl) appear to react at the diffusion-controlled rate, but those bearing electron-withdrawing groups (cyano or nitro) are significantly less reactive. At physiological pH values, the reduction of a DNA guanyl radical involves the transfer of a proton as well as an electron. Comparison of the kinetic results with literature thermodynamic data suggests that the source of this proton is the complementary base-paired cytosine.
Ly
Anne
A
Department of Radiology, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093-0610, USA.
Tran
Nancy Q
NQ
Ward
John F
JF
Milligan
Jamie R
JR
D020029:Base Pairing / Q000187:drug effects*; D004249:DNA Damage / Q000187:drug effects; D005609:Free Radicals; D006147:Guanine / Q000737:chemistry / Q000378:metabolism*; D007211:Indoles / Q000494:pharmacology*; D007700:Kinetics; D010084:Oxidation-Reduction; D010957:Plasmids / Q000378:metabolism; D011522:Protons; D013816:Thermodynamics
D005609:Free Radicals; D007211:Indoles; D011522:Protons; D006147:Guanine