PURIFICATION AND CHARACTERIZATION OF AN IRON SUPEROXIDE-DISMUTASE FROM THE NITROGEN-FIXING AZOTOBACTER-VINELANDII

Two electrophoretically distinct forms of superoxide dismutase (SOD; E C 1.15.1.1) which show different inhibition patterns to hydrogen perox ide have been identified in Azotobacter vinelandii. The SOD inhibited by hydrogen peroxide was purified to homogeneity, and turned out to be an iron superoxide dismutase, The enzyme is present in only one molec ular form with an isoelectric point of 4.1, and it is composed of two identical subunits with an apparent molecular weight of 21,000 Da, Spe ctroscopic analyses indicated that this enzyme contains ferric iron (1 .4-1.6 mol/mol protein) in the typical high-spin form present in other prokaryotic Fe-SODs, N-Terminal sequence alignments (up to the 49th r esidue) showed that A, vinelandii Fe-SOD has high similarity with othe r prokaryotic Fe-SODs.