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Catalytic Site Atlas Search Results
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Catalytic Site Atlas

CSA LITERATURE entry for 1xqd

E.C. name
SpeciesFusarium oxysporum (Fungus)
E.C. Number (IntEnz) 1.7.99.7
CSA Homologues of 1xqd
CSA Entries With UniProtID
CSA Entries With EC Number 1.7.99.7
PDBe Entry 1xqd
PDBSum Entry 1xqd
MACiE Entry 1xqd

Literature Report

IntroductionCytochrome P450 nitric oxide reductase (P450nor) is found in denitrifying organisms such as Fusarium oxysporum. It is a member of the cytochrome P450 superfamily, which are heme-thiolate enzymes. There are two isoforms of P450nor in F. oxysporum, one of which uses NADH as cofactor exclusively, while the other uses NADH or NADPH.
P450nor catalyses the NAD(P)H-dependent reduction of two molecules of the free radical, nitric oxide (NO), to nitrous oxide (N2O). The reaction is unusual because it involves direct electron transfer, in the form of a hydride, from NAD(P)H to a redox protein (heme) that contains only a one-electron redox centre.
P450nor appears to have an important role in protecting the fungus from NO inhibition of mitochondria and other cellular damage that may result from the reaction of NO with other molecules such as oxygen or superoxide to form biologically hazardous compounds.
MechansimA molecule of NO binds to the resting state enzyme, where the heme iron is in its ferric (Fe3+) state, to form an [Fe3+ NO] complex.
This is reduced to form the intermediate thought to be [Fe3+ NO 2H+]. Reduction occurs by hydride transfer from NAD(P)H, and the addition of a proton, derived from the bulk solvent and probably transferred via a hydrogen bonding network involving [Solvent Water – Asp393 – Wat – Ser286 – Wat] to the heme.
NAD(P)+ is rapidly released from the active site, and the intermediate reacts with another molecule of NO to regenerate the enzyme and form N2O and water.
Reaction

Catalytic Sites for 1xqd

Annotated By Reference To The Literature - Site 2 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
SerA286286macie:sideChainSer286 is involved in forming a delivery pathway of a proton from the bulk solvent to the heme iron to yield the reaction intermediate.
AspA393393macie:sideChainAsp393 is involved in forming a delivery pathway of a proton from the bulk solvent to the heme iron to yield the reaction intermediate.

Literature References

Notes:Thr243 is thought to be important in enzyme activity, but it is not known whether it is involved in catalysis or not.
Oshima R
Structural evidence for direct hydride transfer from NADH to cytochrome P450nor.
J Mol Biol 2004 342 207-217
PubMed: 15313618
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