Nucleic Acids Research, 1992, Vol. 20, No. 18 4847-4851
© 1992
CHEMISTRY |
Photooxidation of d(TpG) by phthalocyanines and riboflavin. Isolation and characterization of dinucleoside monophosphates containing the 4R* and 4S* d iastereoisomers of 4,8-di hyd ro-4-hydroxy-8-oxo-2'-deoxyguanosine
Laboratoire des Lésions des Acides Nucléiques, DRFMC/SESAM, Centre d'Etudes Nucléaires de Grenoble 85 X, F-38041 Grenoble Cedex, France
*To whom correspondence should be addressed
Received June 8, 1992. Revised August 20, 1992. Accepted August 20, 1992.
Phthalocyanine mediated photosensitization of 2'-deoxyguanosine (dG) in oxygen saturated aqueous solution has previously been shown to result in the addition of molecular oxygen to the guanine base generating the 4R* and 4S* diastereoisomers of 4,8-dlhydro-4-hydroxy-8-oxo-2'-deoxyguanosine (dO) (the asterisk denotes unambiguous assignment of the 4R and 4S diastereoisomers). The data presented here show that the same guanine modified bases are generated in a 1:1 ratio when thymidylyl (3' ,5')-2'-deoxyguanosine (d(TpG)) is similarly photooxidized. These modified dinucleoside monophosphates, labelled d(TpO)-A and -B, have been isolated by high performance liquid chromatography and characterized by proton NMR spectrometry, fast atom bombardment mass spectrometry, and enzymatic digestions. Photosensitization in D2 instead of H2 leads to an increase in the rate of d(TpO) formation that is consistent with a type II (singlet oxygen) reaction mechanism. Three interesting properties of these modified dinucleoside monophosphates are: i) the rate of their digestion with spleen phosphodiesterase is greatly reduced relative to d(TpG), ii) they are not digested by snake venom phosphodiesterase, and iii) they are stable to 1.0 M piperidine at 90°C for 30 mm. The latter observation indicates that 4,8-dihydro-4-hydroxy-8-oxoguanine is not a base lesion responsible for the strand breaks observed following hot piperidine treatment of DNA exposed to type II photosensitizers or chemically generated singlet oxygen.
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