The nitrate reductase enzyme complex allows Bradyrhizobium sp. USDA 3045 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. Inhibited by micromolar concentrations of azide. Heterotrimer composed of an alpha, a beta and a gamma chain. Alpha and beta are catalytic chains; gamma chains are involved in binding the enzyme complex to the cytoplasmic membrane. Induced by anaerobiosis, there is no significant expression in an aerobic environment. Expression is further induced in the presence of nitrate or nitrite. Belongs to the prokaryotic molybdopterin-containing oxidoreductase family.