The metalloenzyme superoxide dismutase (SOD) catalyses the conversion of superoxide radical anion to oxygen and hydrogen peroxide (McCord

Molecular Infectious Diseases Groupf Department of Paediatrics, Imperial College of Science, Technology and Medicine, S t Mary's Hospital, London Copperand zinc-containing superoxide dismutases ([Cu,Zn]-SODS) are generally considered almost exclusively eukaryotic enzymes, protecting the cytosol and extracellular compartments of higher organisms from damage by oxygen free-radicals. The recent description of a few examples of bacterial forms of the enzyme, located in the periplasm of different Gram-negative micro-organisms, prompted a re-evaluation of this general perception. A PCRbased approach has been developed and used successfully to identify bacterial genes encoding [Cu,Zn]-SOD in a wide range of important human and animal pathogens members of the Haemophilus, Actinobacillus and Pasteurella (HAP) group, and Neisseria meningitidis. Comparison of [Cu,Zn]-SOD peptide sequences found in Haemophilus ducreyi, Actinobacillus pleuropneumonia e, Actinobacillus actinomycetemcomitans, Pasteurella multocida, and N. meningitidis with previously described bacterial proteins and examples of eukaryotic [Cu,Zn]-SOD has shown that the bacterial proteins constitute a distinct family apparently widely separated in evolutionary terms from the eukaryotic examples. The widespread occurrence of [Cu,Zn]-SOD in the periplasm of bacterial pathogens, appropriately located to dismute exogenously derived superoxide radical anions, suggests that this enzyme may play a role in the interactive biology of organisms with their hosts and so contribute to their capacity to cause disease. W2 lPG, UK