Catalyzes the reduction of quinones. Acts by simultaneous two-electron transfer, avoiding formation of highly reactive semiquinone intermediates and producing quinols that promote tolerance of H(2)O(2). Quinone reduction is probably the primary biological role of ChrR. Can also reduce toxic chromate to insoluble and less toxic Cr(3+). Catalyzes the transfer of three electrons to Cr(6+) producing Cr(3+) and one electron to molecular oxygen without producing the toxic Cr(5+) species and only producing a minimal amount of reactive oxygen species (ROS). Chromate reduction protects the cell against chromate toxicity, but is likely a secondary activity. a quinone + H(+) + NADH = a quinol + NAD(+) a quinone + H(+) + NADPH = a quinol + NADP(+) Cr(6+) + 2 NADH + O2 = Cr(3+) + 2 H(+) + 2 NAD(+) + superoxide Cr(6+) + 2 NADPH + O2 = Cr(3+) + 2 H(+) + 2 NADP(+) + superoxide Binds 1 FMN per subunit. Homotetramer. Dimer of dimers. The tetrameric configuration has a central role in chromate reductase activity. Belongs to the SsuE family.