Raman-assisted crystallography reveals end-on peroxide intermediates in a nonheme iron enzyme

Iron-peroxide intermediates are central in the reaction cycle of many iron-containing biomolecules. We trapped iron(III)-(hydro) peroxo species in crystals of superoxide reductase (SOR), a nonheme mononuclear iron enzyme that scavenges superoxide radicals. X-ray diffraction data at 1.95 angstrom resolution and Raman spectra recorded in crystallo revealed iron-(hydro) peroxo intermediates with the ( hydro) peroxo group bound end-on. The dynamic SOR active site promotes the formation of transient hydrogen bond networks, which presumably assist the cleavage of the iron- oxygen bond in order to release the reaction product, hydrogen peroxide.