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 (By similarity). 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. This reaction produces transiently a minimal amount of the toxic Cr(5+) species and reactive oxygen species (ROS). Chromate reduction protects the cell against chromate toxicity, but is likely a secondary activity (By similarity) (PubMed:10788340). 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. Non-competitively inhibited by sulfate. Optimum pH is 5 for chromate reductase activity. Optimum temperature is 80 degrees Celsius for chromate reductase activity. Homotetramer. Dimer of dimers. The tetrameric configuration has a central role in chromate reductase activity. Belongs to the SsuE family.