This is a second nitrate reductase enzyme which can substitute for the NRA enzyme and allows E.coli to use nitrate as an electron acceptor during anaerobic growth. The alpha chain is the actual site of nitrate reduction. a quinol + nitrate = a quinone + H2O + nitrite Binds 1 [4Fe-4S] cluster per subunit. Binds 1 molybdenum-bis(molybdopterin guanine dinucleotide) (Mo-bis-MGD) cofactor per subunit. Tetramer composed of an alpha, a beta and 2 gamma chains. Alpha and beta are catalytic chains; gamma chain is involved in binding the enzyme complex to the cytoplasmic membrane. Belongs to the prokaryotic molybdopterin-containing oxidoreductase family.