The respiratory membrane-bound nitrate reductase enzyme complex plays a role in generation of metabolic energy by using nitrate as a terminal electron acceptor during anaerobic conditions. 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 cyanide, azide and antimycin A. Enzyme stability is not dependent on salt concentration. Characterized with purified enzyme corresponding to a dimer of NarG and NarH. Optimum pH is 8.2. At 40 degrees Celsius (temperature of natural environment) the optimum pH is 7.9. Optimum temperature is 70 degrees Celsius. Probable multiprotein complex; a catalytic heterodimer of an alpha and beta chain is proposed to associate with additional subunits involved in membrane attachment and electron transfer. By nitrate. Exported by the Tat system. Belongs to the prokaryotic molybdopterin-containing oxidoreductase family.