The unique active site of flavodiiron proteins (FDPs) consists of a non-heme diiron-carboxylate site proximal to a flavin mononucleotide (FMN) cofactor. FDPs serve as the terminal components for reductive scavenging of dioxygen or nitric oxide to combat oxidative or nitrosative stress in bacteria, archaea, and some protozoan parasites. Nitric oxide is reduced to nitrous oxide by the four-electron reduced (FMNH2-FeIIFeII) active site (NOR activity). In order to clarify the NOR mechanism of FDP, we undertook a multi-spectroscopic pre-steady state investigation, including the first M�ssbauer spectroscopic characterizations of diiron redox intermediates in FDPs. We have identified a new transient diferrous-dinitrosyl species that appears to be a proximal precursor to N2O formation. We have also clarified the role of the flavin in the NOR mechanism. Our results complement and extend those previously published on the same FDP (Hayashi, T. et al. Biochemistry 2010  , 49, 7040, and J. Am. Chem. Soc. 2012  , 134, 6878) and can be used to distinguish among proposed NOR mechanisms.

Nitric oxide reductase mechanism of a flavo-diiron protein: Identification of active site intermediates and products

248th National Meeting (2014)

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