Evidence for C-H cleavage by an iron-superoxide complex in the glycol cleavage reaction catalyzed by myo-inositol oxygenase

Gang Xing, Yinghui Diao, Lee M. Hoffart, Eric W. Barr, K. Sandeep Prabhu, Ryan J. Arner, C. Channa Reddy, Carsten Krebs, J. Martin Bollinger

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Abstract

myo-Inositol oxygenase (MIOX) activates O2 at a mixed-valent nonheme diiron(II/III) cluster to effect oxidation of its cyclohexan(1,2,3,4,5, 6-hexa)-ol substrate [myo-inositol(MI)] by four electrons to D-glucuronate. Abstraction of hydrogen from C1 by a formally (superoxo)diiron(III/ III) intermediate was previously proposed. Use of deuterium-labeled substrate, 1,2,3,4,5,6-[2H]6-MI (D6-MI), has now permitted initial characterization of the C-H-cleaving intermediate. The MIOX·1,2,3,4,5,6-[2H]6-MI complex reacts rapidly and reversibly with O2 to form an intermediate, G, with a g = (2.05, 1.98, 1.90) EPR signal. The rhombic g-tensor and observed hyperfine coupling to 57Fe are rationalized in terms of a (superoxo)diiron(III/III) structure with coordination of the superoxide to a single iron. G decays to H, the intermediate previously detected in the reaction with unlabeled substrate. This step is associated with a kinetic isotope effect of ≥5, showing that the superoxide-level complex does indeed cleave a C-H(D) bond of MI.

Original languageEnglish (US)
Pages (from-to)6130-6135
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume103
Issue number16
DOIs
StatePublished - Apr 18 2006

All Science Journal Classification (ASJC) codes

  • General

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