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The flavoprotein FerB of Paracoccus denitrificans binds to membranes, reduces ubiquinone and superoxide, and acts as an in vivo antioxidant

FerB is a flavin mononucleotide (FMN)‐containing NAD(P)H:acceptor oxidoreductase of unknown function that is found in the cytoplasm of the bacterium Paracoccus denitrificans. Based on measurements of fluorescence anisotropy, we report here that recombinant FerB readily binds to artificial membrane vesicles. If ubiquinone is incorporated into the membrane, FerB catalyzes its conversion to ubihydroquinone, which may be followed fluorimetrically (with ferricyanide and pyranine entrapped inside the liposomes) or by HPLC. FerB also reduces exogenously added superoxide or superoxide that has been enzymatically generated by the xanthine/xanthine oxidase system or P. denitrificans membrane vesicles. In whole cells, deficiency of FerB increases sensitivity to methyl viologen, as indicated by a lower growth rate and increased production of reactive aldehydes (by‐products of lipid oxidation). Taken together, these data support a role for FerB in protection of cells against lipid peroxidation‐mediated oxidative stress, and suggest that FerB is a prokaryotic counterpart of mammalian NAD(P)H:quinone oxidoreductase 1.