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 beta chain is an electron transfer unit containing four cysteine clusters involved in the formation of iron-sulfur centers. a quinol + nitrate = a quinone + H2O + nitrite Binds 3 [4Fe-4S] clusters per subunit. Binds 1 [3Fe-4S] cluster 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. Proposed to be coexported with the Tat system-dependent alpha subunit. By nitrate.