Copper-containing nitrite reductase: a DFT study of nitrite and nitric oxide adducts.
Copper-containing nitrite reductases (Cu-NIRs) reduce nitrite to NO. Reported here are DFT (density functional theory) results on models of the Cu-NIR active site bound to nitrite and nitric oxide. The Cu-NIR active site appears to have been designed to exclude N-nitrite binding even though N-O bond cleavage would be equally facile in the N- and O-isomers. The active site also appears to force a side-on coordination of the end-product, nitric oxide. The latter feature has to rely on the sterics of the active site to destabilize, thermodynamically speaking, the Cu-NO adduct; under these conditions, the absence of N-nitrite coordination is proposed to be merely a side-effect. For the Cu(II)-NO adduct, sterical crowding appears to also favour the Cu-NO electromer over Cu(I)-NO+, helping to avoid the potentially damaging chemistry associated with an NO+ moiety. These conclusions are in reasonable agreement with previous conclusions drawn from experiment [Science 304 (2004) 867].
Silaghi-Dumitrescu
Radu
R
Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, UK. rlsila@essex.ac.uk
D020134:Catalytic Domain; D003300:Copper / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D009569:Nitric Oxide / Q000737:chemistry*; D009572:Nitrite Reductases / Q000737:chemistry*; D009573:Nitrites / Q000737:chemistry*; D015203:Reproducibility of Results; D013816:Thermodynamics
D009573:Nitrites; D009569:Nitric Oxide; D003300:Copper; D009572:Nitrite Reductases