DNA strand scission by antitumor antibiotics. Detection of C-4'-hydroxylated abasic sites in DNA.

Detection of C-4'-hydroxylated abasic site in calf thymus DNA was investigated. Upon heating with neutral hydrazine (90 degrees C, 5 min) C-4'-hydroxylated abasic site formed by photo-excited Co(III)bleomycin was converted to the fragments having 3'-phosphoro-3''-pyridazinylmethylate as illustrated on Scheme 1. Subsequent enzymatic digestion of the reaction mixture provided four kinds of pyridazine mononucleotides (1, 2, 3, and 4). The fact that the amount of free bases released from calf thymus DNA corresponded well to the amount of pyridazines indicates this reaction can be used for detection of C-4'-hydroxylated abasic site in DNA. By this assay, we first identified the formation of C-4'-hydroxy abasic sites in calf thymus DNA by neocarzinostatin.