Reactions of the hydroxyl radical with various monomeric components of nucleic acid, and with polynucleotides, were studied by observing the transient absorption of the ·OH adduct species. At neutral pH, the rate constants for the attack of ·OH on monomers were of the order of <tex-math>$5\times 10^{9}\ M^{-1}\ {\rm sec}^{-1}$</tex-math>. The rate constants, per base, for ·OH attack on single-stranded polynucleotides were approximately a factor of 5 lower: these were <tex-math>$1.2\times 10^{9}\ M^{-1}\ {\rm sec}^{-1}$</tex-math>, <tex-math>$1.25\times 10^{9}\ M^{-1}\ {\rm sec}^{-1}$</tex-math>, and <tex-math>$0.9\times 10^{9}\ M^{-1}\ {\rm sec}^{-1}$</tex-math> for poly C, poly U, and poly A, respectively. The double-stranded polynucleotides poly (A + U) and DNA had rate constants, per base, for reaction with ·OH at pH 7, of 0.5 and <tex-math>$0.4\times 10^{9}\ M^{-1}\ {\rm sec}^{-1}$</tex-math>, respectively. Absorption spectra and values of extinction coefficients are presented for the ·OH adducts. It is shown that the absorbing transient product of ·OH attack is the same species in the polymers poly C, poly U, and poly A, as in the corresponding nucleotides CMP, UMP, and AMP. Kinetic and spectral data indicate that ·OH attacks a double-stranded polynucleotide at random base sites; the ·OH adduct spectrum of poly (A + U) is identical in shape and magnitude to a composite average of the poly U and poly A adduct spectra. Secondary and tertiary structure appears to have little effect on ·OH reactivity with polynucleotides.

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