High-Valence Iron Without the Heme

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Science  14 Feb 2003:
Vol. 299, Issue 5609, pp. 973
DOI: 10.1126/science.299.5609.973a

Studies of O2 activation by iron-containing enzymes that bind iron with a heme group, such as the cytochromes, have found firm evidence for intermediate species such as iron-oxo groups. Two reports focus on O2 activation in nonheme mono-iron enzymes, where much of our information has been indirect (see the Perspective by Kovacs). Theoretical work has suggested that the formation of the high-valence FeIV=O would be disfavored in nonheme enzymes. Rohde et al. (p. 1037) present structural and spectroscopic evidence for an FeIV=O intermediate in a nonheme model compound that binds the iron through a macrocyclic ligand. Karlsson et al. (p. 1039) describe the x-ray structures of proposed intermediates in the catalytic pathway of naphthalene dioxygenase, a Rieske nonheme iron dioxygenase that catalyses a cis-dihydroxylation reaction. They find O2 bound side-on to the mononuclear iron in the active site. The molecule is positioned so that the two oxygen atoms could react with the carbon atoms of the substrate double bond in a concerted mechanism.


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