This family includes consists of TorC, a pentahemic c-type cytochrome subunit of periplasmic reductases for trimethylamine-N-oxide (TMAO). The N-terminal half is closely related to tetrahemic NapC (or NirT) subunits of periplasmic nitrate (or nitrite) reductases; some species have both TMAO and nitrate reductase complexes.