title: Evidence for C-H cleavage by an iron-superoxide complex in the glycol cleavage reaction catalyzed by myo-inositol oxygenase.
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 > or =5, showing that the superoxide-level complex does indeed cleave a C-H(D) bond of MI.
authors.affiliation: Department of Biochemistry,Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Gang
authors.initials: G
authors.lastname: Xing
authors.forename: Yinghui
authors.initials: Y
authors.lastname: Diao
authors.forename: Lee M
authors.initials: LM
authors.lastname: Hoffart
authors.forename: Eric W
authors.initials: EW
authors.lastname: Barr
authors.forename: K Sandeep
authors.initials: KS
authors.lastname: Prabhu
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Arner
authors.forename: C Channa
authors.initials: CC
authors.lastname: Reddy
authors.forename: Carsten
authors.initials: C
authors.lastname: Krebs
authors.forename: J Martin
authors.initials: JM
authors.lastname: Bollinger
mesh_terms: D000818:Animals; D002244:Carbon / Q000737:chemistry; D002384:Catalysis; D004578:Electron Spin Resonance Spectroscopy; D006018:Glycols / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry; D007294:Inositol / Q000737:chemistry; D050562:Inositol Oxygenase / Q000737:chemistry*; D051379:Mice; D010782:Photolysis; D013481:Superoxides / Q000737:chemistry*
chemical_list: D006018:Glycols; D013481:Superoxides; D007294:Inositol; D002244:Carbon; D006859:Hydrogen; D050562:Inositol Oxygenase