Effect of nitrate on the level of superoxide dismutase in anaerobically grown Escherichia coli.

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Abstract
The effect of nitrate on the level of superoxide dismutase (SOD) in aerobically or anaerobically grown Escherichia coli was examined. The addition of nitrate did not influence the SOD level in aerobically grown E. coli cells. When E. coli was cultureed anaerobically, the cells grown without nitrate contained only iron-containing SOD (Fe SOD), but the cells grown with nitrate contained in addition to the Fe SOD manganese-containing SOD (MnSOD) and a SOD with a protein moiety which is a hybrid between Fe SOD (hybrid SOD). The total level of SOD in cells grown anaerobically with 20 or 40 mM nitrate was three- to fourfold higher than the level in cells grown without nitrate. Adding tungstate during anaerobic culture with nitrate repressed the formation of Mn SOD and hybrid SOD. Nitrate did not affect the level of SOD in anaerobically grown E. coli mutants deficient in nitrate reductase. Adding nitrite during anaerobic culture did not increase the level of SOD in E. coli cells. These results show that the operation of the nitrate respiration system induced the formation of Mn SOD and hybrid SOD.