EPR SPIN-TRAPPING STUDIES OF THE REACTION OF THE HYDROXYL RADICAL WITH PYRIMIDINE NUCLEOBASES, NUCLEOSIDES AND NUCLEOTIDES, POLYNUCLEOTIDES, AND RNA - DIRECT EVIDENCE FOR SITES OF INITIAL ATTACK AND FOR STRAND BREAKAGE

Spin-trapping experiments with the trap Me3CNO have been employed to identify the radicals formed by reaction of .OH (generated from reaction of H2O2 with a variety of transition-metal ions) with pyrimidine derivatives relevant to nucleic acids. Results for the nucleobases, nucleosides and nucleotides confirm the predominance of attack at the C5 and C6 carbon atoms in the pyrimidine ring. Evidence for subsequent transfer is derived from experiments with poly(U) and other polynucleotides as well as RNA, in which anisotropic spectra from immobilized nitroxide adducts can be distinguished from sharper, isotropic spectra which result from further radical damage [pH dependent for poly(U)] or enzymatic cleavage.