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Synthesis

Enzyme Proves Unconventional

Diiron-containing enzyme cleaves C—H bond in an unexpected way

by Amanda Yarnell
April 25, 2006

Proving that nature still has surprises up its sleeve, scientists have discovered an unconventional strategy for cleaving C?H bonds in an iron-containing oxygenase enzyme. 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).

"This is another case where nature throws chemists a curve and says, 'There's more chemistry out there that you haven't thought about,' " comments bioinorganic chemist Lawrence Que Jr. of the University of Minnesota, Minneapolis-St. Paul.

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