Ferric and ferrous ions: binding to DNA and influence on radiation-induced processes

The role of the two principal oxidation states of iron ions in modifying the response of DNA to ionising radiation depends not only on their contrasting redox character but also on their abilities to induce different conformational changes to the helix. Circular dichroism and linear dichroism studies presented here reveal that Fe(III) induces major stereochemical effects in comparison to Fe(II). This is attributed not only to the charge difference but also to their electronic structure that determines the sites of binding of both iron ions to DNA. It seems that Fe(III), which induces strong changes in the helix geometry, is involved in binding to interior base sites. The influence of Fe(II) is much weaker, thus it is probably preferentially localised at the backbone of DNA strands. Hitherto this has not been unambiguously confirmed experimentally. These stereochemical effects have significant consequences for radiation-induced processes and the electron transfer pathway in this vital biopolymer. (C) 2003 Elsevier Ltd. All rights reserved.