Dinucleoside monophosphates in which the 5' nucleoside contained a radiation-modified base were tested as substrates to bovine spleen phosphodiesterase (SPD) and snake venom phosphodiesterase. The radiation-modified bases included thymine glycols, 5-hydroxymethyluracil, 8-hydroxyguanine, and a formamido remnant of thymine. The lesions had widely different effects on diesterase action, varying from little inhibition, as in the case of digestion of dT*pA by SPD, where T* is the hydroxymethyluracil modification, to severe inhibition, as in the case of digestion of dG*pC by SPD, where G* is the 8-hydroxyguanine modification.
The mediation of radiation-induced damage to dinucleoside monophosphate by oxygen and by glutathione was studied. The sequence isomers d(TpA) and d(ApT) were X-irradiated in aqueous solutions and the products isolated by reverse-phase high-performance liquid chromatography. The main products were characterized by proton NMR spectroscopy. In the presence of oxygen the principal products are the formamido derivative formed by breakdown of thymine and the aldehyde derivative formed at the 5' end of the dinucleoside monophosphate, both nucleoside monophosphates and free bases. In the presence of glutathione, the two stereoisomers of the 5,6-dihydrothymine derivatives are prominent. Radiation-induced damage to d(TpA) and d(ApT) in the solid state was also studied.
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