Chemical analysis of DNA alterations: III. Isolation and characterization of adenine oxidation products obtained from oligo- and monodeoxyadenylic acids treated with hydroxyl radicals

Abstract

Oligo- and monodeoxyadenylic acid as well as adenosine and adenine are oxidized by H 2O 2 at concentrations less than 0.1 M and at a pH of 7.4 at the N-7 position of the base moiety leading to adenine-7-N- oxide derivatives. At H 2O 2 concentrations higher than 0.1 M and at pH 8.0 two additional products are formed, which have been identified as 8-hydroxy- and 2-hydroxyadenine. The production, isolation and the methods leading to the chemical characterization of these products are described. Adenine-7-N- oxide was found to be sensitive to ultraviolet light, yielding adenine and 8-hydroxyadenine. The 7-N- oxide of dAMP, whose production and isolation from dAMP is also described, is as stable against 1 M HCl or NaOH as dAMP itself. The oxidation of dAMP to the 7-N- oxide and the liberation of adenine-7-N- oxide from the deoxynucleotide are two independent reactions, as is shown kinetically. Adenine-7-N- oxide was found to be among the reaction products of X-irradiated aqueous solutions of adenine representing the effect of OH radicals. The three oxidation products, being base analogs, were tested for their ability to induce point mutations in the phage T4. All three were found not to be mutagenic base analogs in the test system which, however, does not rule out their significance for the induction of mutations when formed within the DNA of a multiplying organism. 7-methyl- and 7-ethylguanine have also been shown not to induce revertants in phage T4 mutants when added to the growth media, yet they are believed to be responsible for the point mutagenic effect of methyl- and ethylmethanesulfonate, respectively.