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A polarographic study of the catalytic mechanism of the iron-containing superoxide dismutase from Escherichia coli

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Abstract

The dependence of the activity of iron-containing superoxide dismutase from Escherichia coli on pH and ionic strength was investigated extensively in the ranges 7.7–11.0 and 0.02–0.25 M respectively. The results show that the enzymatic activity diminishes with both increasing pH and increasing ionic strength, reaching a minimum value at about pH 11. The activity decrease with increasing pH was ascribed to a gradual titration, by OH ion, of the acid group Fe3+-H2O. This gives rise to a deprotonated enzymatic form with a residual activity which is about 10% that of the protonated form. The dependence of the activity on ionic strength was interpreted as a Debye-Hückel effect.

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