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Iron-containing and manganese-containing superoxide dismutases were found in Plectonema boryanum. The Mn-enzyme occupies about 10% of total activity. The Fe-enzyme was purified to near homogeneity. It contains 2 atoms of iron per mol. Its molecular weight is 41,700 and it is composed of two subunits of identical molecular weight without disulfide linkage. Amino acid composition is presented. Electron paramagnetic resonance spectrum revealed that iron occurs in a high spin ferric form and in some anisotropic environment. The absorption spectrum and the absence of acid-labile enzymes are insensitive to cyanide. Although the Fe-enzyme is sensitive to hydrogen peroxide, the Mn-enzyme is not.
Asada et al. (Tue,) studied this question.