Hydrolysis of carcinogen-dna adducts by three classes of deoxyribonucleosidase to their corresponding bases

We have investigated three different enzymes, each of which splits the glycosidic bonds of normal deoxyribonucleosides, for their ability to cleave acid-sensitive carcinogen-DNA adducts: Leishmania donovani purine deoxyribonucleosidase; Lactobacillus helveticus trans-N-deoxyribosyiase; and purine nucleoside phosphorylase. Twenty-eight substrates were assayed using one or more of the enzymes, monitoring free base formation by reverse-phase HPLC and a diode array detector. Products were characterized by their retention times and UV spectra. The deoxyribonucleosidase showed the broadest specificity: substrates cleaved by either the trans-N-deoxyribosylase or the phosphorylase were hydrolyzed by the deoxyribonucleosidase. O⁶-and N²-alkyldeoxyguanosine, N⁶-alkyl deoxyadenosine and several cyclic adducts were all hydrolyzed by the deoxyribonucleosidase. None of these enzymes cleaved three bulkier adducts; N²-, N⁶- and C-8 derivatives of benzo[a]pyrene, benzo[c]phenanthrene and N-acetoxy-2-acetylamlnofluorene, respectively. Only the deoxyribonucleosidase hydrolyzed O⁶-methyldeoxyguanosine while both the deoxyribonucleosidase and trans-N-deoxyribosylase cleaved N⁶-methyl deoxyadenosine. These enzymes, especially the deoxyribonucleosidase, provide mild ways to release the carcinogen-modified base from deoxyribose and will be useful in DNA adducts analysis.