DNA degradation by the mixture of copper and catechol is caused by DNA-copper-hydroperoxo complexes, probably DNA-Cu(I)OOH

Free hydroxyl radicals (free . OH), singlet oxygen (O-1(2)), or . OH produc ed by DNA-copper-hydroperoxo complexes are possible DNA-damaging reactive o xygen species (ROS) in the reaction system containing copper, catechol, and DNA. para-Chlorobenzoic acid (pCBA) degradation studies revealed that CuCl 2 mixed with catechol produced free . OH. In the presence of DNA, however, inhibition of the pCBA degradation suggested that another ROS is responsibl e for the DNA degradation. Of a series of ROS scavengers investigated, only Kl, NaN3, and Na-formate-all of the salts tested-strongly inhibited the DN A degradation, suggesting that the ionic strength rather than the reactivit y of the individual scavengers could be responsible for the observed inhibi tion. The ionic strength effect was confirmed by increasing the concentrati on of phosphate buffer, which is a poor . OH scavenger, and was interpreted as the result of destabilization of DNA-copper-hydroperoxo complexes. Pipe ridine-labile site patterns in DNA degraded by copper and catechol showed t hat the mixture of Cu(II) and catechol degrades DNA via the intermediate fo rmation of a DNA-copper-hydroperoxo complex. Replacement of guanine by 7-de azaguanine did not retard the DNA degradation, suggesting that the DNA-copp er-hydroperoxo complexes do not bind to the guanine N-7 as proposed in the literature. Environ. (C) 2000 Wiley-Liss, Inc.