<p>This entry represents subunit D (NuoD) of NADH-quinone oxidoreductase (<db_xref db="EC" dbkey="1.6.99.5"/>), and subunit H (NdhH) of NAD(P)H-quinone oxidoreductase (<db_xref db="EC" dbkey="1.6.5.-"/>). NADH-quinone (Q) oxidoreductase is a large and complex redox proton pump, which utilises the free energy derived from oxidation of NADH with lipophilic electron/proton carrier Q to translocate protons across the membrane to generate an electrochemical proton gradient [<cite idref="PUB00045442"/>]. Subunit D (NuoD) is a 49kDa polypeptide that appears to be evolutionarily important in determining the physiological function of complex I/NDH-1 [<cite idref="PUB00045442"/>].</p>