<p>In Proteobacteria and Actinobacteria the main nitrite reductase activity is contributed by the NADH-dependent nitrite reductase, which detoxifies the nitrite formed as the product of nitrate reduction. The NADH-nitrite reductase operon consists of 4 genes: nirB, nirD, nirC and cysG. The enzyme is formed by the two subunits nirB and nirD. NirC is a nitrite transporter and cysG is required for the synthesis of sirohaem, a cofactor of the nirB subunit [<cite idref="PUB00043673"/>, <cite idref="PUB00043674"/>]. NirD displays some sequence similarities with the 2Fe-2S Rieske domain (see <db_xref db="PROSITEDOC" dbkey="PDOC00177"/>), but it does not contain the essential residues for the coordination of the iron sulphur.</p> Nitrite reductase [NAD(P)H] large subunit, NirD bacterial-type