This family is a tetra-haem cytochrome involved in the oxidation of ammonia. It is found in both phototrophic and denitrifying bacteria.

1: Amino acid sequences of cytochrome c-554(548) and cytochrome c' from a halophilic denitrifying bacterium of the genus Paracoccus. Ambler RP, Daniel M, McLellan L, Meyer TE, Cusanovich MA, Kamen MD; Biochem J. 1987;248:365-371. PMID:2829828

2: Heme packing motifs revealed by the crystal structure of the tetra-heme cytochrome c554 from Nitrosomonas europaea. Iverson TM, Arciero DM, Hsu BT, Logan MS, Hooper AB, Rees DC; Nat Struct Biol. 1998;5:1005-1012. PMID:9808046

3: High-resolution structures of the oxidized and reduced states of cytochrome c554 from Nitrosomonas europaea. Iverson TM, Arciero DM, Hooper AB, Rees DC; J Biol Inorg Chem. 2001;6:390-397. PMID:11372197