Cytochromes

Cytochromes can be defined as electron or protontransfer proteins having one or several haem groups. Cytochromes can be classified according to their haem iron coordination, by haem type, and further by sequence similarity (see [1] for nomenclature recommendations). Some haemoproteins, such as P450s and nitric oxide synthase (NOS), have been termed `cytochromes' as well [2]. Although both P450s and NOS can be considered as btype cytochromes, their main function is catalysis. The recommended name for the group of enzymes which includes P450s and NOS is `haem-thiolate proteins' [1]. For further reading on cytochromes, see [2-7].

Haem iron coordination	Axial iron ligands	Protein class
Hexacoordinate	N_His; N_His	Cytochrome c oxidase haem a (`cyt a') Cytochrome b/b₆ Cytochrome b₅ Cytochromes c (Class III and IV) Cytochrome c₅₅₄ (haems 3 and 4) Cytochrome cd₁ nitrite reductase (cdomain) Hydroxylamine oxidoreductase (haems c)
Hexacoordinate	N_His; N_His	Cytochrome c₅₅₄ (haem 1)
Hexacoordinate	N_His; S_Met	Soluble cytochrome b₅₆₂ Cytochromes c (cyt c₁, Class I, IIb, and IV)
Hexacoordinate	N_His; N_Tyr	Cytochrome f
Hexacoordinate	N_His; O_Tyr	Cytochrome cd₁ nitrite reductase (d₁domain)
Hexacoordinate	S_Met; S_Met	Bacterioferritin (cyt b₁; cyt b₅₅₇)
Pentacoordinate / Hexacoordinate	N_His; O₂, CO, NO, CN¯ or other ligand	Cytochrome c oxidase haem a₃ (`cyt a₃') Cytochrome c₅₅₄ (haem 2) Cytochrome c' Hydroxylamine oxidoreductase (haem P460)

Haem type	Protein class
Haem a	Cytochrome c oxidase
Haem b	Cytochromes b
Haem c	Cytochromes c Hydroxylamine oxidoreductase
Haem d	Cytochromes d
Haem d₁	Cytochrome cd₁ nitrite reductase (d₁domain)
Haem o	Cytochrome o oxidase
Haem P460	Hydroxylamine oxidoreductase

PRINTS ID	PRINTS AC	PROSITE/BLOCKS ID	PROSITE AC	BLOCKS AC
Cytochromes
Cytochrome oxidases
-	-	COX1	PS00077	BL00077
Cytochromes b
BACFERRITIN	PR00601	BACTERIOFERRITIN	PS00549	BL00549
-	-	CYTOCHROME_B_HEME CYTOCHROME_B_QO	PS00192 PS00193	BL00192
CYTOCHROMEB5	PR00363	CYTOCHROME_B5	PS00191	BL00191
-	-	CYTOCHROME_B559	PS00537	BL00537
NIHGNASECYTB	PR00161	NI_HGENASE_CYTB_1 NI_HGENASE_CYTB_2	PS00882 PS00883	BL00882
-	-	SDH_CYT_1 SDH_CYT_2	PS01000 PS01001	BL01000
Cytochromes c
CYTOCHROMEC1	PR00603	CYTOCHROME_C	PS00190	BL00190
CYTCHRMECIAB	PR00604
CYTCHROMECIC	PR00605
CYTCHROMECID	PR00606
CYTCHROMECIE	PR00607
CYTCHROMECII	PR00608
CYTOCHROMEC3	PR00609
CYTOCHROMEF	PR00610

PROMISE ID	Description
BACFERRITIN	Bacterioferritin (aka cytochrome b₁ and cytochrome b₅₅₇)
COX	Cytochrome c oxidase
CYTB5	Cytochrome b₅ family
CYTB562	Soluble cytochrome b₅₆₂
CYTBHBL	Cytochrome b/b₆ (b_Hb_L)
CYTC1	Cytochrome c₁
CYTC554	Tetrahaem cytochrome c₅₅₄ from Nitrosomonas europaea
CYTCD1	Cytochrome cd₁ nitrite reductase (cytochrome oxidase)
CYTCI	Class I cytochromes c (mitochondrial cyt c, cyt c₂, cyt c₄, cyt c₅, cyt c554, cyt c₆, cyt c₈)
CYTCII	Class II cytochromes c (cyt c', cyt c556)
CYTCIII	Class III cytochromes c (bacterial multihaem cytochromes: cyt c₃, cyt c₇, HMC)
CYTCIV	Class IV cytochromes c (photosynthetic reaction centre cyt c subunit)
CYTF	Cytochrome f
HAO	Hydroxylamine oxidoreductase

Haem type	Protein family
Haem a	Cytochrome c oxidase
Haem b	Bacterioferritin (cytochrome b₁) Cytochrome b/b₆ Cytochrome b₅ family Soluble cytochrome b₅₆₂
Haem c	Class I cytochromes c Class II cytochromes c Class III cytochromes c Class IV cytochromes c Cytochrome c₁ Cytochrome cd₁ nitrite reductase Cytochrome f