In gram-negative bacteria, cytoplasmic and periplasmic isozymes of superoxide dismutase (SOD) is their defense system against superoxide anion (O2-). In E.coli, there are several SOD isozymes which are manganese-cofactored (MnSOD), iron-cofactored (FeSOD) and copper, zinc-cofactored (CuZnSOD) in perplasm, and they can be generated by autooxidation of dihydromenaquinone in the cytoplasmic membrane. In E.coli, MnSOD and FeSOD have similar structure and kinetic, but CuZnSOD is monomeric. FeSOD is the only SOD in E.coli under anaerobic conditions. MnSOD is induced by environmental stress condition as well as aerobic growth. CuZnSOD is induced in stationary phase. SOD will catalyze the superoxide anion to form oxygen and H2O2. With increasing concentration of H2O2, catalase such as cryptic adenine deaminase is induced in E.coli to degrade H2O2 into water and oxygen.

Superoxide Radicals Degradation References