Within the NapC/NirT family of cytochrome c proteins, some members, such as NapC Swiss:P33932 and NirT Swiss:P24038, bind four haem groups, while others, such as TorC Swiss:P33226, bind five haems. This family aligns the common N-terminal region that contains four haem-binding C-X(2)-CH motifs.

1: Electron transfer and binding of the c-type cytochrome TorC to the trimethylamine N-oxide reductase in Escherichia coli. Gon S, Giudici-Orticoni MT, Mejean V, Iobbi-Nivol C; J Biol Chem 2001;276:11545-11551. PMID:11056172

2: The napEDABC gene cluster encoding the periplasmic nitrate reductase system of Thiosphaera pantotropha. Berks BC, Richardson DJ, Reilly A, Willis AC, Ferguson SJ; Biochem J 1995;309:983-992. PMID:7639719

3: TMAO anaerobic respiration in Escherichia coli: involvement of the tor operon. Mejean V, Iobbi-Nivol C, Lepelletier M, Giordano G, Chippaux M, Pascal MC; Mol Microbiol 1994;11:1169-1179. PMID:8022286