“…NapA contains one molybdopterin cofactor and one [4Fe-4S] cluster (González, Correia, Moura, Brondino, & Moura, 2006;Romão, Dias, & Moura, 2001). In D. desulfuricans, the nap operon includes the napCMADGH genes (Marietou, Richardson, Cole, & Mohan, 2005), where NapGH are membrane-associated ironsulphur proteins that form a quinol dehydrogenase module (Brondijk, Fiegen, Richardson, & Cole, 2002;Kern & Simon, 2008); NapC is a membrane-associated tetrahaem cytochrome of the NapC/NrfH family, which acts as a quinol dehydrogenase (Rodrigues, Pereira, & Archer, 2011;Simon, 2002); NapD is a cytoplasmic maturation protein that may be involved in the insertion of the molybdenum cofactor into NapA (Dow et al, 2014); and NapM is a tetrahaem c-type cytochrome that is the probable direct electron donor to NapA, a role played by NapB in other bacteria (Marietou et al, 2005). The exact order of the electron transfer chain between the menaquinol and nitrate has not been established, nor if the NapC and NapGH systems are both essential.…”