Superoxide Dismutase from Escherichia coli B

Superoxide dismutase, which catalyzes the disproportionation of univalently reduced oxygen (O2.- + O2.- + 2H+ → O2 + H2O2) and which has previously been demonstrated in a variety of mammalian sources, has now been purified from Escherichia coli. Whereas the mammalian enzyme is blue and contains copper and zinc, the bacterial superoxide dismutase is red-purple and was found to contain manganese. The molecular weight of the E. coli enzyme was found to be 39,500 by sedimentation equilibrium and was shown, by gel electrophoresis in the presence of sodium dodecyl sulfate, to be composed of two subunits of equal size. Electron paramagnetic resonance spectrometry and chemical analysis demonstrated between 1.6 and 1.8 atoms of manganese per molecule of enzyme. The enzyme contains no significant amounts of copper or zinc. The ultraviolet and visible absorption spectra of the enzyme are presented, as are the results of amino acid analysis.