Cytochrome c, class IA/ IB (IPR002327)

Short name: Cyt_c_1A/1B

Overlapping homologous superfamilies


Family relationships



Cytochromes c (cytC) can be defined as electron-transfer proteins having one or several haem c groups, bound to the protein by one or, more generally, two thioether bonds involving sulphydryl groups of cysteine residues. The fifth haem iron ligand is always provided by a histidine residue. CytC possess a wide range of properties and function in a large number of different redox processes.

Ambler [PMID: 1646017] recognised four classes of cytC.

Class I includes the low-spin soluble cytC of mitochondria and bacteria, with the haem-attachment site towards the N terminus, and the sixth ligand provided by a methionine residue about 40 residues further on towards the C terminus. On the basis of sequence similarity, class I cytC were further subdivided into five classes, IA to IE. Class IB includes the eukaryotic mitochondrial cyt C and prokaryotic 'short' cyt C2 exemplified by Rhodopila globiformis cyt C2; Class IA includes 'long' cyt C2, such as Rhodospirillum rubrum cyt C2 and Aquaspirillum itersonii cyt C-550, which have several extra loops by comparison with Class IB cyt C.

The 3D structures of a considerable number of class IA and IB cytC have been determined. The proteins consist of 3-6 alpha-helices; the three most conserved 'core' helices form a 'basket' around the haem group, with one haem edge exposed to the solvent. Most class I cytC have conserved aromatic residues clustered around the haem and axial ligands.

GO terms

Biological Process

No terms assigned in this category.

Molecular Function

GO:0009055 electron transfer activity
GO:0020037 heme binding

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.