Reductive repression in Escherichia coli K-12 is mediated by oxygen radicals

Cyclic AMP (cAMP) content and the expression of cAMP-dependent phenotypes were positively correlated with respiration capacity in respiration-deficient mutants of Escherichia coli K-12 ("reductive repression," R. Hertz, and J. Bar-Tana, (1982) Arch. Biochem. Biophys. 213, 193-199). Reductive repression in respiration-deficient mutants could not be accounted for by respective changes in either the energy charge of adenine nucleotides or the redox state of pyridine nucleotides but could be ascribed to an increased formation of oxygen radicals under conditions of limited respiration. Scavengers of superoxide radicals eliminated reductive repression in respiration-deficient mutants with a concomitant increase in cAMP content. Such scavengers also effected a partial escape from permanent glucose catabolite repression, thus indicating a possible role played by oxygen radicals in both repression modes.