title: Iron incorporation into MnSOD A (bacterial Mn-dependent superoxide dismutase) leads to the formation of a peroxidase/catalase implicated in oxidative damage to bacteria.
abstract: BACKGROUND
  Mn/Fe-superoxide dismutase (SOD) is a family of enzymes essential for organisms to be able to cope with oxygen. These enzymes bound to their classical metals catalyze the dismutation of the free radical superoxide anion (O2(-)) to H2O2 and molecular oxygen. E. coli has the manganese-dependent SOD A and the iron-dependent SOD B.
  
  
  METHODS
  Strains of E. coli overexpressing SOD A or SOD B were grown in media with different metal compositions. SODs were purified and their metal content and SOD activity were determined. Those proteins were incubated with H2O2 and assayed for oxidation of Amplex red or o-phenylenediamine, consumption of H2O2, release of iron and protein radical formation. Cell survival was determined in bacteria with MnSOD A or FeSOD A after being challenged with H2O2.
  
  
  RESULTS
  We show for the first time that the bacterial manganese-dependent SOD A when bound to iron (FeSOD A) has peroxidase activity. The in vivo formation of the peroxidase FeSOD A was increased when media had higher levels of iron because of a decreased manganese metal incorporation. In comparison to bacteria with MnSOD A, cells with FeSOD A had a higher loss of viability when exposed to H2O2.
  
  
  CONCLUSIONS
  The biological occurrence of this fundamental antioxidant enzyme in an alternative iron-dependent state represents an important source of free radical formation.
authors.affiliation: Free Radical Metabolites Group, Immunity, Inflammation & Disease Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA. Electronic address: ganinidasilvad@niehs.nih.gov.
authors.forename: Douglas
authors.initials: D
authors.lastname: Ganini
authors.affiliation: Protein Expression Core Facility, Genome Integrity & Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Petrovich
authors.affiliation: Protein Expression Core Facility, Genome Integrity & Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.
authors.forename: Lori L
authors.initials: LL
authors.lastname: Edwards
authors.affiliation: Free Radical Metabolites Group, Immunity, Inflammation & Disease Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.
authors.forename: Ronald P
authors.initials: RP
authors.lastname: Mason
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D001426:Bacterial Proteins / Q000502:physiology*; D002374:Catalase / Q000502:physiology*; D007501:Iron / Q000502:physiology*; D009195:Peroxidase / Q000502:physiology*; D013482:Superoxide Dismutase / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; D007501:Iron; D002374:Catalase; D009195:Peroxidase; C095500:SodA protein, Bacteria; C087504:SodB protein, Bacteria; D013482:Superoxide Dismutase
keywords: Free radical; Iron; Manganese; Metal; Peroxidase; Superoxide dismutase (SOD)