DNA-DAMAGE BY TERT-BUTOXYL RADICALS GENERATED IN THE PHOTOLYSIS OF A WATER-SOLUBLE, DNA-BINDING PEROXYESTER ACTING AS A RADICAL SOURCE

The photolysis of the water-soluble perester a. leads to tert-butoxyl radicals as confirmed by EPR studies with the spin trap 5,5-dimethylpy rroline N-oxide (DMPO). In the presence of DNA, oxidative cleavage of the latter was demonstrated by the formation of strand breaks in super coiled pBR 322 DNA and by a substantial decrease of the melting temper ature of salmon. testes DNA. Guanidine, released from, for example, ox azolone and oxoimidazolidine on base treatment, was observed with calf thymus DNA and 2'-deoxyguanosine. These DNA modifications were effect ively inhibited by the radical scavenger di-tert-butylcresol or the hy drogen atom donor glutathione. Photosensitization by the arene chromop hore was excluded since the corresponding ester 2 caused no DNA damage , nor were the photoproducts of the perester 1 active. The efficacy of the perester 1 in oxidizing DNA derives from the fact that the tert-b utoxyl radicals are photolytically generated in the immediate vicinity of the DNA, due to electrostatic binding of the cationic perester to the DNA, as confirmed by fluorescence measurements. These results demo nstrate that the photolysis of perester 1 provides a suitable source o f tert-butoxyl radicals in aqueous media, a necessary prerequisite for biochemical investigations.