Calculating Structures

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Science  31 Mar 2000:
Vol. 287, Issue 5462, pp. 2377
DOI: 10.1126/science.287.5462.2377c

Methane monooxygenase hydroxylase is a dinuclear iron-containing enzyme that converts methane and dioxygen into methanol and water. The structures of the oxidized and reduced enzymes have been determined by x-ray crystallography, but detailed structural information is lacking for intermediates in the catalytic cycle. Dunietz et al. have performed ab initio calculations of this system using density functional theory. At 100 atoms, their model is significantly larger and more complex than previous ab initio studies of this and other transition metal-containing enzymes. On the basis of their model, the authors proceed to ascribe an unassigned electron density to a structurally important water molecule in the x-ray structure of the reduced enzyme. Their structures of the two key catalytic intermediates, Hperoxo and Q, differ from models previously proposed in the literature, but can be reconciled with existing experimental data. Hydrogen bonds involving water molecules are critical elements in both intermediates, and the hydrogen bonding network surrounding the active site serves to constrain the diiron and ligand geometries. More extensive calculations with a larger number of atoms may help to define the pathways between these intermediates.—JU

J. Am. Chem. Soc. in press

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