It seems to function in response to environmental stress when various electron transfer chains are affected or when the environment is highly oxidizing. It reduces quinones to the hydroquinone state to prevent interaction of the semiquinone with O2 and production of superoxide. It prefers NADH over NADPH. a quinone + H(+) + NADH = a quinol + NAD(+) a quinone + H(+) + NADPH = a quinol + NADP(+) Binds 1 FMN per monomer. Homodimer and homotetramer; in equilibrium. Cells lacking this gene show no phenotypes, however, N-trichloromethyl-mercapto-4-cyclohexene-1,2-dicarboximide and 8-hydroxyquinoline significantly inhibit the growth of the wrbA knockout relative to the wild-type, which is consistent with a role for WrbA in protecting against environmental stressors through its quinone reductase activity. FMN promotes WrbA association into tetramers, which are more thermoresistant than dimers or monomers, suggesting that multimerization underlies the FMN effect on WrbA thermostability. Belongs to the WrbA family. Was originally (PubMed:9694845) thought to enhance the formation and/or stability of non-covalent complexes between the trp repressor protein and operator-bearing DNA. However, WrbA does not specifically influence the affinity or mode of binding of TrpR to its operator.