<p>The nitrate reductase enzyme (<db_xref db="EC" dbkey="1.7.99.4"/>) is composed of three subunits; an alpha, a beta and two gamma. It is the second nitrate reductase enzyme which it can substitute for the NRA enzyme in <taxon tax_id="562">Escherichia coli</taxon> allowing it to use nitrate as an electron acceptor during anoerobic respiration [<cite idref="PUB00008262"/>].</p> <p>Nitrate reductase gamma subunit resembles cytochrome b and transfers electrons from quinones to the beta subunit [<cite idref="PUB00008245"/>].</p>