Catalyzes the reduction of quinones (PubMed:14766567). 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 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 (PubMed:14766567, PubMed:17088379, PubMed:22558308). Can also reduce potassium ferricyanide, 2,6-dichloroindophenol, V(5+), Mo(6+), methylene blue, cytochrome c and U(6+) (PubMed:14766567, PubMed:17088379). During chromate reduction, is able to use both NAD or NADP equally well (PubMed:14766567). 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. May be inhibited by divalent cations. kcat is 3.7 sec(-1) with chromate as substrate (at pH 5 and 35 degrees Celsius) (PubMed:14766567). kcat is 29 sec(-1) with uranyl as substrate (at pH 7 and 37 degrees Celsius) (PubMed:17088379). kcat is 30 sec(-1) with chromate as substrate (at pH 7 and 37 degrees Celsius) (PubMed:17088379). Optimum pH is 5. Optimum temperature is 35 degrees Celsius. Homotetramer. Dimer of dimers. The tetrameric configuration has a central role in chromate reductase activity. Induced by both chromate and the stationary phase. Cells lacking this gene show an increased sensitivity to chromate. Belongs to the SsuE family.