Escherichia coli expresses a copper- and zinc-containing superoxide dismutase

A mutant of Escherichia coli, unable to produce manganese- or iron-containing superoxide dismutase (SOD), was found to contain modest levels of an SOD that was judged to be a copper- and zinc-containing SOD on the basis of inhibition by cyanide and inactivation by either H2O2 or diethyldithiocarbamate. Moreover, the diethyldithiocarbamate-inactivated enzyme could be reactivated with Cu(II), and this reconstituted enzyme, like the native enzyme, was unaffected by EDTA and was inhibited by cyanide. This enzyme was, furthermore, selectively released by osmotic shock, in keeping with a periplasmic localization, and it was strongly induced during aerobic growth. This enzyme was also present in the SOD-competent parental strain. Failure to detect it previously can be attributed to its periplasmic localization, thermal lability, sensitivity to pH, and to its relative paucity. It will now be interesting to explore the phenotypic consequences imposed by the absence of this SOD.