Effect of metal ions on the anaerobic synthesis of superoxide dismutase in Escherichia coli.

Abstract

The effect of various metal ions on the anaerobic synthesis of superoxide dismutase (SOD) in Escherichia coli was examined. When cells were grown anaerobically by fermentation, adding CuSO4 in the culture medium resulted in the synthesis of manganese-containing SOD (Mn SOD), but adding CrCl3, CoCl2, NiSO4, ZnSO4 or Ga(N03)3 did not. The presence of nitrate in culture medium stimulated the anaerobic synthesis of Mn SOD by CuSO4. During the incubation of resting cells under anaerobic conditions, the addition of CuSO4 and KNO3 increased Mn SOD activity, which was inhibited by chloramphenicol. Adding CrCl3 or Ga(N03)3 with KNO3 increased Mn SOD activity during anaerobic incubation of resting cells, but adding MnCl2, (NH4)2Fe(S04)2, K3Fe(CN)6, CoCl2, NiSO4 or ZnSO4 with KNO3 did not increase Mn SOD activity. Instead, they decreased it. The increase of Mn SOD activity in resting cells by Cr ions or Ga ions with nitrate was inhibited by ferric citrate but that by Cu ions was not. When cells were grown anaerobically with CuSO4 or when resting cells were incubated anaerobically with CuSO4, a new activity band of SOD appeared in the polyacrylamide gel electrophoreogram, regardless of the operation of nitrate respiration. The SOD of the new activity band was insensitive to cyanide, H2O2 or diethyldithiocarbamate. This new SOD and Mn SOD had the same molecular size but had different charges.Escherichia coil has three types of superoxide dismutase (SOD): iron-containing SOD (Fe SOD) (20), manganese-containing SOD (Mn SOD) (7), and a SOD which consists of one of each of the subunits from the other two isozymes and contains both iron and manganese (Hybrid SOD) (2, 3).