<p>The nitrate reductase enzyme complex allows bacteria to use nitrate as an electron acceptor during anaerobic growth. The enzyme complex is a heterotrimer consisting of alpha, beta and gamma subunits [<cite idref="PUB00017048"/>]. The alpha subunit contains a molybdenum cofactor, the beta subunit contains [Fe-S] clusters while the gamma subunit contains haem and is membrane bound. The alpha and beta subunits form a membrane extrinsic catalytic dimer which is bound to the membrane by the gamma subunit, which is a b-type cytochrome that receives electrons from the quinone pool and transfers them to the beta subunit. The three subunits form a stable "flower"-shaped structure [<cite idref="PUB00017049"/>], where the gamma subunit anchors the alpha and beta subunits to the membrane through predominantly hydrophobic interactions. The structure is further stabilised by the presence of a phosphatidylglycerol molecule that is bound by all three subunits. The alpha subunit uses a Mo-bisMGD cofactor for catalytic activity and, like other proteins that bind this cofactor, forms four alpha-beta domains grouped around the cofactor. Interaction with the other catalytic subunit occurs along an extensive, buried interface.</p>