F. E. Jenney, . Jr, M. F. Verhagen, X. Cui, A. et al., Anaerobic Microbes: Oxygen Detoxification Without Superoxide Dismutase, Science, vol.286, issue.5438, pp.306-309, 1999.
DOI : 10.1126/science.286.5438.306

M. Lombard, M. Fontecave, D. Touati, and V. Nivière, Reaction of the Desulfoferrodoxin from Desulfoarculus baarsii with Superoxide Anion: EVIDENCE FOR A SUPEROXIDE REDUCTASE ACTIVITY, Journal of Biological Chemistry, vol.275, issue.1, pp.115-121, 2000.
DOI : 10.1074/jbc.275.1.115
URL : https://hal.archives-ouvertes.fr/hal-01075803

V. Nivière and M. Fontecave, Discovery of superoxide reductase: an historical perspective, Journal of Biological Inorganic Chemistry, vol.9, issue.2, pp.119-123, 2004.
DOI : 10.1007/s00775-003-0519-7

D. M. Kurtz and . Jr, Microbial Detoxification of Superoxide:?? The Non-Heme Iron Reductive Paradigm for Combating Oxidative Stress, Accounts of Chemical Research, vol.37, issue.11, pp.902-908, 2004.
DOI : 10.1021/ar0200091

J. S. Valentine, D. L. Wertz, T. J. Lyons, L. L. Liou, J. J. Goto et al., The dark side of dioxygen biochemistry, Current Opinion in Chemical Biology, vol.2, issue.2, pp.253-262, 1998.
DOI : 10.1016/S1367-5931(98)80067-7

M. D. Clay, F. E. Jenney, . Jr, P. L. Hagedoorn, G. N. George et al., Superoxide Reductase:?? Implications for Active-Site Structures and the Catalytic Mechanism, Journal of the American Chemical Society, vol.124, issue.5, pp.788-805, 2002.
DOI : 10.1021/ja016889g

T. Jovanovic, C. Ascenso, K. R. Hazlett, R. Sikkink, C. Krebs et al., Neelaredoxin, an Iron-binding Protein from the Syphilis Spirochete, Treponema pallidum, Is a Superoxide Reductase, Journal of Biological Chemistry, vol.275, issue.37, pp.28439-28448, 2000.
DOI : 10.1074/jbc.M003314200

T. Santos-silva, J. Trincao, A. L. Carvalho, C. Bonifacio, F. Auchère et al., The first crystal structure of class III superoxide reductase from Treponema pallidum, JBIC Journal of Biological Inorganic Chemistry, vol.1, issue.Pt A, pp.548-558, 2006.
DOI : 10.1007/s00775-006-0104-y

A. Coelho, P. Matias, V. Fülöp, A. Thompson, A. Gonzalez et al., Desulfoferrodoxin structure determined by MAD phasing and refinement to 1.9-?? resolution reveals a unique combination of a tetrahedral FeS 4 centre with a square pyramidal FeSN 4 centre, Journal of Biological Inorganic Chemistry, vol.2, issue.6, pp.680-689, 1997.
DOI : 10.1007/s007750050184

V. Adams, A. Royant, V. Nivière, F. P. Molina-heredia, and D. Bourgeois, Structure of Superoxide Reductase Bound to Ferrocyanide and Active Site Expansion upon X-Ray-Induced Photo-Reduction, Structure, vol.12, issue.9, pp.1729-1740, 2004.
DOI : 10.1016/j.str.2004.07.013

J. P. Emerson, D. E. Cabelli, D. M. Kurtz, and . Jr, An engineered two-iron superoxide reductase lacking the [Fe(SCys)4] site retains its catalytic properties in vitro and in vivo, Proceedings of the National Academy of Sciences, vol.100, issue.7, pp.3802-3807, 2003.
DOI : 10.1073/pnas.0537177100

C. Mathé, V. Nivière, and T. A. Mattioli, Fe3+?????2???peroxo species in superoxide reductase from Treponema pallidum. Comparison with Desulfoarculus baarsii, Biophysical Chemistry, vol.119, issue.1, pp.38-48, 2006.
DOI : 10.1016/j.bpc.2005.06.013

C. Mathé, V. Nivière, and T. A. Mattioli, Is Associated with pH Dependent Spectral Changes, Journal of the American Chemical Society, vol.127, issue.47, pp.16436-16441, 2005.
DOI : 10.1021/ja053808y

T. L. Poulos, The role of the proximal ligand in heme enzymes, Journal of Biological Inorganic Chemistry, vol.1, issue.4, pp.356-359, 1996.
DOI : 10.1007/s007750050064

A. Dey, T. Okamura, N. Ueyama, B. Hedman, K. O. Hodgson et al., Sulfur K-Edge XAS and DFT Calculations on P450 Model Complexes:?? Effects of Hydrogen Bonding on Electronic Structure and Redox Potentials, Journal of the American Chemical Society, vol.127, issue.34, pp.12046-12053, 2005.
DOI : 10.1021/ja0519031

I. Lin, E. B. Gebel, T. E. Machonkin, W. M. Westler, and J. Markley, Changes in hydrogen-bond strengths explain reduction potentials in 10 rubredoxin variants, Proceedings of the National Academy of Sciences, vol.102, issue.41, pp.14581-14586, 2005.
DOI : 10.1073/pnas.0505521102

M. D. Clay, J. P. Emerson, E. D. Coulter, D. M. Kurtz, J. Jr et al., Spectroscopic characterization of the [Fe(His)4(Cys)] site in 2Fe-superoxide reductase from Desulfovibrio vulgaris, Journal of Biological Inorganic Chemistry, vol.8, issue.6, pp.671-682, 2003.
DOI : 10.1007/s00775-003-0465-4

J. P. Emerson, E. D. Coulter, R. S. Phillips, D. M. Kurtz, and . Jr, Kinetics of the Superoxide Reductase Catalytic Cycle, Journal of Biological Chemistry, vol.278, issue.41, pp.39662-39668, 2003.
DOI : 10.1074/jbc.M306488200

T. Kitagawa, A. Dey, P. Lugo-mas, J. B. Benedict, W. Kaminsky et al., A Functional Model for the Cysteinate-Ligated Non-Heme Iron Enzyme Superoxide Reductase (SOR), Journal of the American Chemical Society, vol.128, issue.45, pp.14448-14449, 2006.
DOI : 10.1021/ja064870d

I. G. Denisov, T. M. Makris, S. G. Sligar, and I. Schlichting, Structure and Chemistry of Cytochrome P450, Chemical Reviews, vol.105, issue.6, pp.2253-2277, 2005.
DOI : 10.1021/cr0307143

*. We and . Dr, Vincent Favaudon for assistance with pulse radiolysis experiments

S. Ménage-for-assistance-with, E. Spectroscopy, D. N. , and C. B. , Danièle Touati for her help in E. coli complementation tests This work was supported by grants from the CEA, programme " Toxicologie Nucléaire C.O.W. acknowledges a Post-doctoral fellowship from the CEA program Toxicologie Nucléaire

. Abbreviations and . Sor, superoxide reductase; FTIR, Fourier transform infrared; RR, resonance Raman; EPR, electron paramagnetic resonance; Fpr, flavodoxin reductase from Escherichia coli, FIGURE LEGENDS Figure, vol.4