Nitric oxide reductase (NOR) isolated from Fusarium oxysporum catalyzes the reduction reaction of nitric oxide (NO) to nitrous oxide (N 2 O). In this reaction, the transient reaction intermediate (t=∼20 s) is produced by the reduction of ferric-NO complex with NADH. To elucidate the electronic structure of the intermediate, we measured its resonance Raman spectrum using the continuous-flow method. From these spectral features, we have concluded that the electronic structure of the intermediate in the NO reduction reaction by fungal NOR is Fe 2+ NO − H + . Further, we have found that the Ser286/Asp393 hydrogen-bond network is the proton pathway to the active site on the basis of crystallographic and mutagenesis studies. From these results, we discuss the molecular mechanism of NO reduction reaction catalyzed by fungal NOR.
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