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 language||English (US)|
|Number of pages||6|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Apr 18 2006|
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