Evidence for C-H cleavage by an iron-superoxide complex in the glycol cleavage reaction catalyzed by myo-inositol oxygenase.
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.
Xing
Gang
G
Department of Biochemistry,Pennsylvania State University, University Park, PA 16802, USA.
Diao
Yinghui
Y
Hoffart
Lee M
LM
Barr
Eric W
EW
Prabhu
K Sandeep
KS
Arner
Ryan J
RJ
Reddy
C Channa
CC
Krebs
Carsten
C
Bollinger
J Martin
JM
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*
D006018:Glycols; D013481:Superoxides; D007294:Inositol; D002244:Carbon; D006859:Hydrogen; D050562:Inositol Oxygenase