beta subunit of nitrate reductase A (NarH) and similar proteins
This subfamily includes nitrate reductase A, a member of the DMSO reductase family. The respiratory nitrate reductase complex (NarGHI) from E. coli is a heterotrimer, with the catalytic subunit (NarG) with a molybdo-bis (molybdopterin guanine dinucleotide) cofactor and an [Fe-S] cluster, the electron transfer subunit (NarH) with four [Fe-S] clusters, and the integral membrane subunit (NarI) with two b-type hemes. Nitrate reductase A often forms a respiratory chain with the formate dehydrogenase via the lipid soluble quinol pool. Electron transfer from formate to nitrate is coupled to proton translocation across the cytoplasmic membrane generating proton motive force by a redox loop mechanism. Demethylmenaquinol (DMKH2) has been shown to be a good substrate for NarGHI in nitrate respiration in E. coli.
Jiyao W et al.(2023). "The conserved domain database in 2023.",