Effect of Hydrogen Peroxide on the Iron-Containing Superoxide Dismutase of 'Escherichia coli'

摘要

The iron-containing superoxide dismutase from Escherichia coli is inactivated by hydrogen peroxide H2O2 to a limit of approx 90%. The superoxide dismutase activity remaining after treatment with H202 differed from the activity of the native enzyme with respect to heat stability, inhibition by azide, and inactivation by light in the presence of rose bengal and by N-bromosuccinimide. The native and the H2O2 modified enzymes were indistinguishable by electrophoresis on polyacrylamide gels. Inactivation of the enzyme by H2O2 was accompanied by loss of tryptophan and some loss of iron, but there was no detectable loss of histidine or of other amino acids. H2O2 treatment caused changes in the optical spectrum of the enzyme. Inactivation of the enzyme by h2O2 depends upon the iron at the active site. Thus, the apoenzyme and the manganese-substituted enzyme were unaffected by H2O2. The authors conclude that reaction of H2O2 with the iron at the active site generates a potent oxidant capable of attacking tryptophan residues. A mechanism is proposed.