A heterotrimeric protein complex which is involved in electron transport during anaerobic respiration. In E. coli electrons are passed from the FdnGHI complex to the NarGHI complex via menoquinone and menaquinol. Within NarGHI, electrons are passed from the two heme molecules in the NarI subunit down a Fe-S cluster chain in the NarH and NarG subunits to the Molybdenum cofactor, Mo-bisMGD, in the NarG subunit.