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PDBsum entry 3bnh
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Oxidoreductase
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PDB id
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3bnh
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References listed in PDB file
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Key reference
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Title
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Binding and reduction of sulfite by cytochrome c nitrite reductase.
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Authors
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P.Lukat,
M.Rudolf,
P.Stach,
A.Messerschmidt,
P.M.Kroneck,
J.Simon,
O.Einsle.
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Ref.
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Biochemistry, 2008,
47,
2080-2086.
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PubMed id
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Abstract
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Pentaheme cytochrome c nitrite reductase (ccNiR) catalyzes the six-electron
reduction of nitrite to ammonia as the final step in the dissimilatory pathway
of nitrate ammonification. It has also been shown to reduce sulfite to sulfide,
thus forming the only known link between the biogeochemical cycles of nitrogen
and of sulfur. We have found the sulfite reductase activity of ccNiR from
Wolinella succinogenes to be significantly smaller than its nitrite reductase
activity but still several times higher than the one described for
dissimilatory, siroheme-containing sulfite reductases. To compare the sulfite
reductase activity of ccNiR with our previous data on nitrite reduction, we
determined the binding mode of sulfite to the catalytic heme center of ccNiR
from W. succinogenes at a resolution of 1.7 A. Sulfite and nitrite both provide
a pair of electrons to form the coordinative bond to the Fe(III) active site of
the enzyme, and the oxygen atoms of sulfite are found to interact with the three
active site protein residues conserved within the enzyme family. Furthermore, we
have characterized the active site variant Y218F of ccNiR that exhibited an
almost complete loss of nitrite reductase activity, while sulfite reduction
remained unaffected. These data provide a first direct insight into the role of
the first sphere of protein ligands at the active site in ccNiR catalysis.
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