Mechanistic studies of NO reduction in dinuclear metalloproteins

This study investigates mechanisms by which metalloproteins reduce nitric oxide (NO) to nitrous oxide (N₂O), a key step in bacterial denitrification and nitrosative stress resistance. Using spectroscopic techniques, we show that NO binds first to heme iron(II) in terminal oxidases and engineered NOR models, while distal metals stabilize a heme-hyponitrite intermediate rather than directly binding NO. Flavodiiron proteins (FDPs) were also examined; deflavo-FDP retained single-turnover NO reduction, indicating the diiron center catalyzes NO reduction while FMN regenerates the oxidized site. These findings reveal distinct catalytic routes and roles of metal centers in NO reductase activity.