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| {{STRUCTURE_2ppf| PDB=2ppf | SCENE= }} | | {{STRUCTURE_2ppf| PDB=2ppf | SCENE= }} |
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| '''Reduced mutant D98N of AfNiR exposed to nitric oxide'''
| | ===Reduced mutant D98N of AfNiR exposed to nitric oxide=== |
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| ==Overview==
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| Nitrite reductase (NiR) is an enzyme that uses type 1 and type 2 copper sites to reduce nitrite to nitric oxide during bacterial denitrification. A copper-nitrosyl intermediate is a proposed, yet poorly characterized feature of the NiR catalytic cycle. This intermediate is formally described as Cu(I)-NO+ and is proposed to be formed at the type 2 copper site after nitrite binding and electron transfer from the type 1 copper site. In this study, copper-nitrosyl complexes were formed by prolonged exposure of exogenous NO to crystals of wild-type and two variant forms of NiR from Alcaligenes faecalis (AfNiR), and the structures were determined to 1.8 A or better resolution. Exposing oxidized wild-type crystals to NO results in the reverse reaction and formation of nitrite that remains bound at the active site. In a type 1 copper site mutant (H145A) that is incapable of electron transfer to the type 2 site, the reverse reaction is not observed. Instead, in both oxidized and reduced H145A crystals, NO is observed bound in a side-on manner to the type 2 copper. In AfNiR, Asp98 forms hydrogen bonds to both substrate and product bound to the type 2 Cu. In the D98N variant, NO is bound side-on but is more disordered when observed for the wild-type enzyme. The solution EPR spectra of the crystallographically characterized NiR-NO complexes indicate the presence of an oxidized type 2 copper site and thus are interpreted as resulting from stable copper-nitrosyls and formally assigned as Cu(II)-NO-. A reaction scheme in which a second NO molecule is oxidized to nitrite can account for the formation of a Cu(II)-NO- species after exposure of the oxidized H145A variant to NO gas.
| | The line below this paragraph, {{ABSTRACT_PUBMED_17924665}}, adds the Publication Abstract to the page |
| | (as it appears on PubMed at http://www.pubmed.gov), where 17924665 is the PubMed ID number. |
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| | {{ABSTRACT_PUBMED_17924665}} |
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| ==About this Structure== | | ==About this Structure== |
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| [[Category: Nitrite reductase]] | | [[Category: Nitrite reductase]] |
| [[Category: Oxidoreductase]] | | [[Category: Oxidoreductase]] |
| ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun May 4 13:35:08 2008'' | | |
| | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jul 28 19:09:07 2008'' |
