Substrate activation for O2 reactions by oxidized metal centers in biology

Monita Y.M. Pau, John D Lipscomb, Edward I. Solomon

Research output: Contribution to journalReview article

69 Citations (Scopus)

Abstract

The uncatalyzed reactions of O2 (S = 1) with organic substrates (S = 0) are thermodynamically favorable but kinetically slow because they are spin-forbidden and the one-electron reduction potential of O2 is unfavorable. In nature, many of these important O2 reactions are catalyzed by metalloenzymes. In the case of mononuclear non-heme iron enzymes, either FeII or FeIII can play the catalytic role in these spin-forbidden reactions. Whereas the ferrous enzymes activate O2 directly for reaction, the ferric enzymes activate the substrate for O 2 attack. The enzyme-substrate complex of the ferric intradiol dioxygenases exhibits a low-energy catecholate to FeIII charge transfer transition that provides a mechanism by which both the Fe center and the catecholic substrate are activated for the reaction with O2. In this Perspective, we evaluate how the coupling between this experimentally observed charge transfer and the change in geometry and ligand field of the oxidized metal center along the reaction coordinate can overcome the spin-forbidden nature of the O2 reaction.

Original languageEnglish (US)
Pages (from-to)18355-18362
Number of pages8
JournalProceedings of the National Academy of Sciences of the United States of America
Volume104
Issue number47
DOIs
StatePublished - Nov 20 2007

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Metals
Enzymes
Dioxygenases
Iron
Electrons
Ligands

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Substrate activation for O2 reactions by oxidized metal centers in biology. / Pau, Monita Y.M.; Lipscomb, John D; Solomon, Edward I.

In: Proceedings of the National Academy of Sciences of the United States of America, Vol. 104, No. 47, 20.11.2007, p. 18355-18362.

Research output: Contribution to journalReview article

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N2 - The uncatalyzed reactions of O2 (S = 1) with organic substrates (S = 0) are thermodynamically favorable but kinetically slow because they are spin-forbidden and the one-electron reduction potential of O2 is unfavorable. In nature, many of these important O2 reactions are catalyzed by metalloenzymes. In the case of mononuclear non-heme iron enzymes, either FeII or FeIII can play the catalytic role in these spin-forbidden reactions. Whereas the ferrous enzymes activate O2 directly for reaction, the ferric enzymes activate the substrate for O 2 attack. The enzyme-substrate complex of the ferric intradiol dioxygenases exhibits a low-energy catecholate to FeIII charge transfer transition that provides a mechanism by which both the Fe center and the catecholic substrate are activated for the reaction with O2. In this Perspective, we evaluate how the coupling between this experimentally observed charge transfer and the change in geometry and ligand field of the oxidized metal center along the reaction coordinate can overcome the spin-forbidden nature of the O2 reaction.

AB - The uncatalyzed reactions of O2 (S = 1) with organic substrates (S = 0) are thermodynamically favorable but kinetically slow because they are spin-forbidden and the one-electron reduction potential of O2 is unfavorable. In nature, many of these important O2 reactions are catalyzed by metalloenzymes. In the case of mononuclear non-heme iron enzymes, either FeII or FeIII can play the catalytic role in these spin-forbidden reactions. Whereas the ferrous enzymes activate O2 directly for reaction, the ferric enzymes activate the substrate for O 2 attack. The enzyme-substrate complex of the ferric intradiol dioxygenases exhibits a low-energy catecholate to FeIII charge transfer transition that provides a mechanism by which both the Fe center and the catecholic substrate are activated for the reaction with O2. In this Perspective, we evaluate how the coupling between this experimentally observed charge transfer and the change in geometry and ligand field of the oxidized metal center along the reaction coordinate can overcome the spin-forbidden nature of the O2 reaction.

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