title: Hydroxyl radical-induced strand break formation in single-stranded polynucleotides and single-stranded DNA in aqueous solution as measured by light scattering and by conductivity.
abstract: Combining conductivity measurements and molecular weight determination by means of low-angle laser light scattering, we have found for the polyribonucleotides (polyuridylic acid (poly(U], polyadenylic acid (poly(A], polycytidylic acid (poly(C] and polyguanylic acid (poly(G] and for single-stranded DNA (ssDNA) that, on average, 8.5 counterions per single-strand break (ssb) are liberated under salt-free conditions. This relationship allows us to estimate, from conductivity measurements alone, G-values of single-strand break formation (G(ssb] for the polydeoxyribonucleotides (polydeoxyriboadenylic acid (poly(dA], polydeoxyribocytidylic acid (poly(dC], polydeoxyribothymidylic acid (poly(dT], polydeoxyribouridylic acid (poly(dU] and polydeoxyriboguanylic acid (poly(dG]. The following G(ssb) values (units of mumol J-1) have been obtained for anoxic conditions: poly(dA), 0.23; poly(dC), 0.14; poly(dT), 0.06; poly(dU), 0.046 and poly(dG), 0.009. Time-resolved conductivity measurements in pulse radiolysis enable us to measure the rate of strand break formation. The rate has been found to be similar for poly(dA) and ssDNA over a range of pH values. Poly(dC) and poly(dU) exhibit conductivity increase components with half-lives similar to those of poly(dA) and ssDNA at corresponding pH values. The implications of these results are discussed.
mesh_terms: D004249:DNA Damage; D004277:DNA, Single-Stranded / Q000187:drug effects*; D004553:Electric Conductivity; D005609:Free Radicals; D006878:Hydroxides / Q000494:pharmacology*; D017665:Hydroxyl Radical; D008027:Light; D011131:Polyribonucleotides; D012542:Scattering, Radiation; D012996:Solutions; D014867:Water
chemical_list: D004277:DNA, Single-Stranded; D005609:Free Radicals; D006878:Hydroxides; D011131:Polyribonucleotides; D012996:Solutions; D014867:Water; D017665:Hydroxyl Radical