Regulation of manganese-containing superoxide dismutase in Escherichia coli. Anaerobic induction by nitrate.

We have previously demonstrated that iron plays an important regulatory role in the biosynthesis of manganese-containing superoxide dismutase in Escherichia coli (Moody, C.S., and Hassan, H.M. (1984) J. Biol. Chem. 259, 12821-12825). In this study, we demonstrated that the effect of iron is at the transcriptional/translational level, whereas the effect of manganese is at the post-translational level. The anaerobic additions of nitrate or nitrate plus paraquat caused a positive change in the redox potential of the growth medium and concomitant induction of the manganese-superoxide dismutase in the cells. By using 59Fe, we were able to identify two unique proteins that were constitutively made, but contained iron only under conditions where the synthesis of manganese-superoxide dismutase was fully repressed. The presence of a multicopy plasmid carrying the manganese-superoxide dismutase gene resulted in the anaerobic expression of the gene presumably by neutralizing the limited number of repressor molecules found in the cells. In toto, the data support our previously proposed model for a negatively controlled operon where the repressor molecule is envisioned as an allosteric redox sensing protein. Conditions known to oxidize or to deplete the iron are also found to cause induction of the manganese-superoxide dismutase albeit the absence of dioxygen.