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. Proposed Rieske subunit involved in a protonmotive Q-cycle mechanism-based electron transfer electrons to the beta subunit. Binds 1 [2Fe-2S] cluster per subunit. 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.