Instability of (ara-C) DNA under alkaline conditions

We employed both [5-3H] ara-C and ([2-14C] ara-C labeled L1210 DNA for analysis following exposure to alkali under various conditions. The results demonstrated that the tritium label on C5 of ara-C molecules incorporated in DNA was exchanged with water under alkaline conditions and, therefore, radioactivity was subsequently detectable in the acid-soluble fraction. The [14C] ara-C labeled DNA, however, was not susceptible to loss or radioactivity by this mechanism, and the appearance of this isotope in the acid-soluble fraction required degradation of the DNA strand or pyrimidine ring. Our results indicated that the [14C] labeled DNA was degraded by alkali, suggesting structural instability of this abnormal nucleic acid. These findings provide useful technical information on the purification of (ara-C) DNA labeled with different isotopes.