Has menaquinol-oxidizing activity. HmeA, HmeB and HmeE subunits may together catalyze electron transfer from menaquinol to cytochrome c. Binds 4 [4Fe-4S] clusters. Consists of five subunits: an integral membrane subunit, a cytochrome b-like subunit, a cytochrome c subunit and two iron-sulfur subunits. Predicted to be exported by the Tat system. The position of the signal peptide cleavage has been experimentally proven.