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(NO₃)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(NO₃)₃ with KNO₃ increased Mn SOD activity during anaerobic incubation of resting cells, but adding MnCl₂, (NH₄)₂Fe(SO₄)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.