Bacterial respiratory complex I (proton-translocating NADH:quinone oxidoreductase)

Reusable bacterial module for the conserved 14-subunit respiratory complex I, also called NDH-1 or NADH:quinone oxidoreductase. The peripheral arm oxidizes NADH, transfers electrons through FMN and iron-sulfur centers, and reduces the quinone pool. The membrane arm couples this redox chemistry to proton translocation. The module separates the NADH-input, quinone-reduction, membrane-interface, and antiporter-like proton-pumping parts so that fused subunits such as NuoC/D can be represented without collapsing the enzyme to a single step. It excludes the non-homologous, non-proton-pumping type-II NADH dehydrogenase (Ndh/NDH-2).

Pseudomonas putida KT2440 supplies exact representatives for every bacterial core subunit. PP_4121/Q88FH5 is a single NuoC/D polypeptide and therefore satisfies both conserved C- and D-subunit roles. Eukaryotic supernumerary NDUF subunits are outside this bacterial core module and their absence is not a pathway hole. GO:0050136 denotes non-electrogenic NADH:quinone activity and is incompatible with the defining proton-translocating chemistry of NDH-1; its automated propagation to Nuo subunits should be removed rather than used to model this module.