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Synthesis

Diiron oxygenase cleaves C-H bond in an unexpected way

May 1, 2006 | A version of this story appeared in Volume 84, Issue 18

An iron-containing oxygenase has been found to use an unconventional strategy for cleaving C−H bonds. J. Martin Bollinger Jr., Carsten Krebs, and coworkers at Pennsylvania State University report that the enzyme myo-inositol oxygenase (MIOX) operates by a mechanism different from that of related diiron enzymes. The pair of iron atoms in MIOX uses O2 to cleave a single C−H bond in the cellular messenger molecule myo-inositol to produce d-glucuronate (shown). The researchers find that MIOX starts its catalytic cycle with one iron as Fe(II) and the other as Fe(III), unlike all of its diiron oxygenase brethren, which start with both irons in the +2 oxidation state (Biochemistry 2006, 45, 5393 and 5402). This suggests that MIOX's Fe(II)/Fe(III) cofactor is unlikely to go on to generate the high-valent Fe(IV)=O species its relatives use to oxidize their substrates, Bollinger says. The researchers proved their hunch by using deuterium-labeled substrate and electron paramagnetic resonance spectroscopy, showing that the oxygenating species in MIOX is in fact an Fe(III)/Fe(III) superoxide species (Proc. Natl. Acad. Sci. USA 2006, 103, 6130).

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