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 (PubMed:15840577). 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 (PubMed:14766567, PubMed:15840577). Can also reduce potassium ferricyanide and 2,6-dichloroindophenol (PubMed:14766567). During chromate reduction, displays an eightfold preference for NADH over NADPH (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 930 sec(-1) with benzoquinone as substrate (at pH 7.5 and 70 degrees Celsius) (PubMed:15840577). kcat is 440 sec(-1) with menaquinone as substrate (at pH 8.0 and 60 degrees Celsius) (PubMed:15840577). kcat is 25 sec(-1) with duroquinone as substrate (at pH 8.0 and 70 degrees Celsius) (PubMed:15840577). kcat is 6.4 sec(-1) with coenzyme Q1 as substrate (at pH 8.5 and 60 degrees Celsius) (PubMed:15840577). kcat is 5.8 sec(-1) with chromate as substrate (at pH 5 and 70 degrees Celsius) (PubMed:14766567). Optimum pH is 5 for chromate reductase activity. Optimum temperature is 70 degrees Celsius for chromate reductase activity. Homotetramer. Dimer of dimers. The tetrameric configuration has a central role in chromate reductase activity. Induced by H(2)O(2) (PubMed:15840577). Induced by both chromate and the stationary phase (PubMed:14766567). Cells lacking this gene are inhibited by chromate to a greater extent than the wild-type. Belongs to the SsuE family.