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The DNA-cleaving activity of auromomycin (AUR) was prevented by the free radical scavengers alpha-tocopherol and isopropanol. Participation of a free radical in DNA strand scission by AUR and macromomycin (MCR) was confirmed by electron spin resonance (ESR) spectroscopy, using spin trapping technique. In the mixture of AUR and the spin-trap, phenyl N-tert-butyl nitron (PBN), a definite signal was observed in the presence of ethanol or methanol, and addition of dithiothreitol increased the signal intensity about 5-fold, giving a hyperfine coupling constant of aN = 15.9 G and a beta H = 3.6 G. MCR exhibited no distinct signals in the same reaction mixture, but addition of dithiothreitol induced signals with ESR parameters similar to those of AUR. 2-Mercaptoethanol did not significantly affect the appearance and intensity of the ESR spectra generated by MCR or AUR. Chromophores, extracted from MCR and AUR, showed spectra similar to those of native MCR and AUR. The intensity of ESR signals parallels the degree of DNA strand scission by MCR, AUR and their free chromophores, suggesting that a free radical generated by these antibiotics is involved in the DNA breakage reaction. The ESR parameters of AUR or MCR radical adduct with spintraps were compared to .OH, .O2- or CH3CHOH adduct, suggesting that the free radical formed in the presence of ethanol is CH3CHOH. A plausible intermediate radical species, generated by the antibiotics and transferred to ethanol, may be .OH (hydroxyl radical). The current experiments present evidence for involvement of free radical(s) in DNA breakage by macromomycin and auromomycin, although the precise radical species has not been identified.

Evidence for involvement of a free radical in DNA-cleaving reaction by macromomycin and auromomycin.