Free Radical Processes in g- and Heavy Ion Irradiated DNA
EMSL Project ID
2546
Abstract
An understanding of the radiation-induced free radical mechanisms in DNA is important to the elucidation of the ultimate effects of ionizing radiation on DNA (Becker and Sevilla, 1993). One largely free radical-induced lesion that is a critical radiation-damage end point in DNA, is the double strand break (dsb). If a dsb is associated with other nearby radiation damage in a clustered multiple damage site, the break will often not be repairable (Ward et al. 1995). The two focuses of this proposal are (1) to explicate the free radical pathways that lead to strand breaks and (2) to determine the spatial distribution of free radical formation near the chemically relevant sites, in order to search for and investigate clustered damage. In g-irradiated DNA approximately half of the ionizations occur at the bases and half on the sugar phosphate backbone. Because of the energetics of damage transfer, it is unlikely that base damage would transfer to the sugar-phosphate backbone and result in strand breaks; it would be desirable to know exactly which free radicals are present on the backbone and what type of clustered damage is present. With regard to the identity of the backbone free radicals, it has been proposed that the C1', C3' and/or C4' radicals are formed at 77 K when hydrated DNA is irradiated with with g-, O-16 and Ar-36/40 radiation (Becker et al. 1996, Razskazovskii et al. 1996, Weiland and H??ttermann 1999, Debije and Bernhard 2001 ). These radicals result from net loss of a hydrogen atom from each respective site, likely through deprotonation of a deoxyribose radical cation. We have also recently observed two important radical species which are formed by rupture of the C3'???O bond and a P???O bond respectively and are, therefore, accompanied by immediate strand breaks. These radicals are, likely, formed through dissociative electron attachment and their existence lends support to a newly proposed mechanism for strand break formation in DNA (Bouda??ffa et al. 2002). A full characterization of all these radicals is necessary in order to fully understand radiation damage processes in DNA.One objective of this proposal is to use ENDOR methods to fully characterize the hydrogen hyperfine coupling constants of the backbone radicals; samples; in heavy ion irradiated samples, suc radicals can constitute up to 60% of the radicals present, thus, characterization is more straightforward than in g-irradiated samples. With knowledge of the relevant hyperfine coupling constants, observation and characterization of the same radicals in g-irradiated samples will be facilitated. The second objective of this proposed project is to use pulsed ESR techniques to characterize the clustering of damage in both g-irradiated and heavy ion irradiated DNA, especially complex clustering that occurs with a sugar moiety radical present and which makes strand break repair difficult Thus the use of the pulsed EPR/ENDOR facilities at the EMSL is critical to the completion of this work. We anticipate the need for 400 hours of Pulsed EPR/ENDOR/ELDOR of time and request such. ReferencesBECKER, D. AND SEVILLA. M. D.. 1993. In Advances in Radiation Biology (J. T. Lett and W. K. Sinclair, Eds.) pp 121 ??? 180, Academic Press, San Diego.BECKER, D., RAZSKAZOVSKII Y., CALLAGHAN, M. U. AND SEVILLA, M. D. 1996, Radiation Research 146, 361???368.BOUDA??FFA, B., CLOUTIER, P., HUNTING, D., HUELS, M. A. AND SANCHE, L. 2002. Radiation Research 157, 227 ??? 234.DEBIJE, M. G. AND BERNHARD, W. A. 2002, Radiation Research 155, 687-692.RAZSKAZOVSKII, Y., ROGINSKAYA, M. AND SEVILLA, M. D. 1998, Radiation Research 149, 422 ??? 432.WARD, J. F., MILLIGAN, J.R., JONES, G. D. D. AND FAHEY, R. C. 1978, In Radiation Damage in DNA (Fuciarelli, A. and Zimbrick, J. D, Eds.) pp 45-???54, Batelle Press, Columbus, Ohio.WEILAND, B. AND H??TTERMANN, J. 1999, International Journal of Radiation Biology 75, 1169???1175.
Project Details
Project type
Capability Research
Start Date
2003-01-08
End Date
2005-10-05
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members