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The crystal structure of xanthine oxidoreductase during catalysis: implications for reaction mechanism and enzyme inhibition.


ABSTRACT: Molybdenum is widely distributed in biology and is usually found as a mononuclear metal center in the active sites of many enzymes catalyzing oxygen atom transfer. The molybdenum hydroxylases are distinct from other biological systems catalyzing hydroxylation reactions in that the oxygen atom incorporated into the product is derived from water rather than molecular oxygen. Here, we present the crystal structure of the key intermediate in the hydroxylation reaction of xanthine oxidoreductase with a slow substrate, in which the carbon-oxygen bond of the product is formed, yet the product remains complexed to the molybdenum. This intermediate displays a stable broad charge-transfer band at approximately 640 nm. The crystal structure of the complex indicates that the catalytically labile Mo-OH oxygen has formed a bond with a carbon atom of the substrate. In addition, the MoS group of the oxidized enzyme has become protonated to afford Mo-SH on reduction of the molybdenum center. In contrast to previous assignments, we find this last ligand at an equatorial position in the square-pyramidal metal coordination sphere, not the apical position. A water molecule usually seen in the active site of the enzyme is absent in the present structure, which probably accounts for the stability of this intermediate toward ligand displacement by hydroxide.

SUBMITTER: Okamoto K 

PROVIDER: S-EPMC419534 | biostudies-literature | 2004 May

REPOSITORIES: biostudies-literature

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The crystal structure of xanthine oxidoreductase during catalysis: implications for reaction mechanism and enzyme inhibition.

Okamoto Ken K   Matsumoto Koji K   Hille Russ R   Eger Bryan T BT   Pai Emil F EF   Nishino Takeshi T  

Proceedings of the National Academy of Sciences of the United States of America 20040517 21


Molybdenum is widely distributed in biology and is usually found as a mononuclear metal center in the active sites of many enzymes catalyzing oxygen atom transfer. The molybdenum hydroxylases are distinct from other biological systems catalyzing hydroxylation reactions in that the oxygen atom incorporated into the product is derived from water rather than molecular oxygen. Here, we present the crystal structure of the key intermediate in the hydroxylation reaction of xanthine oxidoreductase with  ...[more]

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