The beta chain is an electron transfer unit containing four cysteine clusters involved in the formation of iron-sulfur centers. Electrons are transferred from the gamma chain to the molybdenum cofactor of the alpha subunit. a quinol + nitrate = a quinone + H2O + nitrite Binds 3 [4Fe-4S] clusters per subunit. Binds 1 [3Fe-4S] cluster per subunit.