ESCHERICHIA-COLI EXPRESSES A COPPER-CONTAINING AND ZINC-CONTAINING SUPEROXIDE-DISMUTASE

A mutant of Escherichia coli, unable to produce manganese- or iron-con taining superoxide dismutase (SOD), was found to contain modest levels of an SOD that was judged to be a copper and zinc-containing SOD on t he basis of inhibition by cyanide and inactivation by either H2O2 or d iethyldithiocarbamate. Moreover, the diethyldithiocarbamate-inactivate d enzyme could be reactivated with Cu(II), and this reconstituted enzy me, like the native enzyme, was unaffected by EDTA and was inhibited b y cyanide. This enzyme was, furthermore, selectively released by osmot ic shock, in keeping with a periplasmic localization, and it was stron gly 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, sensiti vity to pH, and to its relative paucity. It will now be interesting to explore the phenotypic consequences imposed by the absence of this SO D.