| Abstract: | Spectroscopic analysis of the reduction of both nitro blue tetrazolium and ferricytochrome c induced by neocarzinostatin shows that superoxide free radical is produced during the spontaneous degradation of the antibiotic. The amount of superoxide free radical produced from neocarzinostatin is not affected by the presence of thiol, although earlier work has shown that DNA damage is stimulated at least 1000-fold by thiol. Transition metals are not involved in this reaction. Although superoxide dismutase inhibits the reduction of nitro blue tetrazolium and cytochrome c induced by neocarzinostatin, neither it nor catalase interferes with the action of neocarzinostatin on DNA, whether or not drug has been activated by thiol. The pH profiles for spontaneous base release and alkali-labile base release (a measure of nucleoside 5'-aldehyde formation at a strand break) do not correspond with that for the generation of superoxide free radical from neocarzinostatin. The same holds for supercoiled DNA cutting by neocarzinostatin chromophore in the absence of a thiol, which is an acid-favored reaction. These results indicate that the generation of superoxide free radical by the drug does not correlate with DNA damage activity, whether or not thiol is present. Furthermore, the failure of hydroxyl free-radical scavengers to inhibit drug-induced single-strand breaks in supercoiled DNA in the absence of thiol also indicates that a diffusible hydroxyl free radical is most probably not involved in this reaction. |
