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The role of superoxide radicals in biological damage in the presence of copper(II) ions has been investigated. Solutions of purified penicillinase in phosphate buffer, saturated with either air N/sub 2/, N/sub 2/O, or N/sub 2/O/O/sub 2/, were..gamma..-irradiated in the presence and in the absence of formate. The residual activity of the enzyme in catalyzing the cleavage of the..beta..-lactam ring of benzylpenicillin, was then monitored. The results indicate that in metal-free systems only the primary water-derived radicals, H,e/sub aq/, and OH, contribute toward enzyme inactivation, while the secondary species O/sub 2/ and CO/sub 2/ do not. The effect of copper(II) ions on the radiation-induced damage depended on which of the active species was predominant. With OH radicals, no effect of copper was detected. The damage originating from e/sub aq/ and H radicals decreased with the addition of copper, presumably due to their trapping by the copper(II) ions. In contrast, with O/sub 2/ radicals predominant in the system, copper dramatically enhanced the damage. This copper-induced sensitization was further increased in the presence of H/sub 2/O/sub 2/ and the dose modifying factor of copper exceeded 100, i.e. enchancement of the damage by two orders of magnitude, as compared with an oxygen enhancement ratiomore » of 2-3 generally found for molecular oxygen. This copper effect could be completely eliminated by EDTA. The present results suggest that the presence of both transition metal ions and H/sub 2/O/sub 2/ and the binding of the metal ions to the target bimolecules are required for the manifestation.« less
Samuni et al. (Tue,) studied this question.