Inductions of Superoxide Dismutases in Escherichia coli

Escherichia coli growing anaerobically respond to NO, with a 3-fold induction of the iron-containing superoxide dismutase. Mutants lacking nitrate reductase do not show this response. Anaerobically grown cells also contain an inactive form of the manganesecontaining superoxide dismutase (MnSOD) which can be activated by addition of Mn(I1) salts in the presence of acidic guanidinium chloride, followed by dialysis against neutral buffer. Direct addition of Mn(I1) to a neutral solution of the inactive MnSOD does not impart activity. This inactive MnSOD thus behaves as would the apoenzyme or the enzyme bearing a metal other than Mn(I1) at its active sites. Terminal electron acceptors, such as NO; or trimethylamine N-oxide, increase the amount of inactive MnSOD produced by anaerobic E. coli. Paraquat, which is itself ineffective in this regard, markedly augments the effect of these terminal electron acceptors. It appears that flow of electrons to sinks such as NO; or trimethylamine N-oxide, facilitated by paraquat, is sufficient to elicit biosynthesis of the MnSOD protein and that 0; is not needed for this process. Yet, oxygenation and concomitant 0; production do appear important for the insertion of manganese into the growing MnSOD polypeptide, possibly because 0; oxidizes Mn(I1) to Mn(III), and the latter is the valence state most effective in combining with the apoenzyme.