Cytochromes a

**Definition:** A subclass of heme a containing cytochromes that have two imidazole nitrogens as axial ligands and an alpha-band absorption of 605 nm. They are found in a variety of microorganisms and in eucaryotes as a low-spin cytochrome component of MITOCHONDRIAL ELECTRON TRANSPORT COMPLEX IV.

**Tree numbers:** - D08.244.175.249 - D12.776.422.220.175.249

**Synonyms:** - Cytochrome a