Excess Electron Transfer in DNA Studied by Pulse Radiolysis and γ-Radiolysis of Naphthalimide and Iodouridine Modified ODN

Abstract

An excess electron was attached to naphthalimide (NI) modified 12-mer oligodeoxynucleotides (ODNs) and the electron transfer in DNA was investigated by monitoring the transient absorption of NI radical anion (NI •- ) during the pulse radiolysis. Formation of the transient absorption of NI •- was observed according to the reaction of e aq - with NI-modified ODN. Only 25% of e aq - reacting with NI-modified ODN were observed by the transient absorption of NI •-, which corresponds to electron transfer over no more than three base pairs, suggesting a low mobility of an electron attached to DNA. Electron transfer in DNA was also studied by γ-radiolysis of ODN containing 5-iododeoxyuridine ( I U) as a second electron acceptor. Electron transfer in DNA was estimated by the protection of dehalogenation of I U offered by NI during the γ-radiolysis of NI- and I U-modified ODNs where the spacing between the NI and I U was varied. The protection effect became very low by the insertion of three or four A−T base pairs between NI and I U. The results driven from both pulse radiolysis and γ-radiolysis experiments were consistent with the low mobility of an excess electron in DNA, which is in strong contrast to the occurrence of the long-range hole transfer in DNA.