Non-enzymatic ATP-mediated binding of hydroxymethyl derivatives of aromatic hydrocarbons to DNA

ATP mediates covalent binding of hydroxymethyl derivatives of aromatic hydrocarbons to DNA. This non-enzymatic reaction has been studied with 6-[¹⁴C]hydroxymethylbenzo[a]pyrene ([¹⁴C]BP-6-CH₂OH) and 7-[¹⁴C]hydroxymethylbenz[a]anthracene ([¹⁴C]BA-7-CH₂OH) at 37°C in Tris buffer (pH 7.0). While ADP mediates the reaction 25-50% as well as ATP, six other possible phosphate donors including AMP were inactive as cofactors. A complex response to ATP occurred in which low binding of BP-6-CH₂OH or BA-7-CH₂OH was observed at concentrations of ATP below 2.5 mM, but a greater than linear response to higher concentrations of ATP was observed until ATP was saturating. Binding of the substrates to RNA was much lower than to DNA. Fluorescence spectra of BP-6-CH₂OH bound to DNA were almost identical to the spectra of 6-bromomethylbenzo[a]pyrene bound to DNA and free 6-methylbenzo[a]pyrene, indicating that ATP-mediated binding of BP-6-CH₂OH to DNA occurs at the 6-methyl group. The fate of ATP and ADP in the binding reaction of BP-6-CH₂OH was examined by thin layer chromatography. Loss of one phosphate group occurs during the reaction. With ATP the rate of loss is about 100-fold greater than the rate of binding of BP-6-CH₂OH to DNA. This implies that the binding reaction proceeds through formation of a presumed reactive and unstable phosphate ester intermediate which then inefficiently binds to DNA.