Radiolysis of DNA in the presence of a protein studied by HPL-gel chromatography

The influence of bovine serum albumin (BSA) on the radiolysis of double-stranded DNA was studied by measuring the loss of highly polymerized DNA with HPL-gel chromatography. The scavenger capacity of BSA for OH.-radicals kBSA [BSA] was kept constant. at 7.8 x 10(5) s-1, when DNA (0.1 mg/ml) was irradiated under different gas conditions (air, N2 and N2O), at pH 7 and 5 and with different ionic conditions. The resulting protein radicals react with DNA producing DNA protein crosslinks and DNA double-strand breaks. The yield and the kind of DNA damage depend on the nature of the protein radicals and their association with DNA. High phosphate concentration prevents the association of BSA with DNA and causes a reduction of the protection by BSA against double-strand break-age of DNA. Radiolysis in the presence of BSA in perchlorate solution leads to more strand breakage and less protein crosslinking than in phosphate solution because perchlorate is more chaotropic than phosphate. Changing the pH from 7 to 5 increases the protection by BSA against DNA strand breakage.