Distribution of Damage in Irradiated 5′-AMP: 8,5′-Cyclo-AMP, 8-Hydroxy-AMP, and Adenine Release

Abstract

The yields of 8,5''-cycloadenosine-5''-monophosphate, 8-hydroxyadenosine-5''-monophosphate and adenine release were measured in aqueous solutions of (5''-AMP) irradiated under N2O. The yields are strongly pH dependent in a way which reflects the pKa of ionizable groups within 5''-AMP. Redistribution of hydroxyl radical attack between base and ribose moieties appears to be occurring in response to changes in the acid-base equilibria of 5''-AMP. Other pH-dependent phenomena which only indirectly reflect the pKa of 5''-AMP include the result that the yield of the (R) epimer of 8,5''-cycloadenosine-5''-monophosphate predominates at low pH while that of the (S) epimer predominates at high pH.