PROSITE documentation PDOC50939
Cytochrome b561 domain profile


Cytochromes b561 constitute a class of intrinsic membrane proteins containing two heme molecules that are involved in ascorbate (vitamin C) regeneration. They have been suggested to function as electron transporters, shuttling electrons across membranes from ascorbate to an acceptor molecule. The one-electron oxidation product of ascorbate, monodehydro-ascorbate (MDHA) has been shown to function as an electon acceptor for mammalian and plant cytochromes b561. The cytochrome b561-catalyzed reduction of MDHA results in the regeneration of the fully reduced ascorbate molecule. Cytochromes b561 have been identified in a large number of phylogenetically distant species, but are absent in prokaryotes. Most species contain three or four cytochrome b561 paralogous proteins [1].

Members of the cytochrome b561 protein family are characterized by a number of structural features, likely to play an essential part in their function. They are highly hydrophobic proteins with six transmembrane helices (named TMH1 through TMH6), four conserved histidine residues, probably coordinating the two heme molecules, and predicted substrate-binding sites for ascorbate and MDHA [1]. The functionally relevant and structurally most conserved region in the cytochrome b561 family is the TMH2 to -5 4-helix core with an amino acid composition that is very well conserved in the inner surface and somewhat less conserved in the outer surface of the core. The two terminal helices (TMH1 and TMH6) are less conserved [2,3].

The profile we developed covers the six transmembrane helices of the cytochrome b561 domain.

Last update:

October 2003 / First entry.


Technical section

PROSITE method (with tools and information) covered by this documentation:

CYTOCHROME_B561, PS50939; Cytochrome b561 domain profile  (MATRIX)


1AuthorsVerelst W. Asard H.
TitleA phylogenetic study of cytochrome b561 proteins.
SourceGenome Biol. 4:R38-R38(2003).
PubMed ID12801412

2AuthorsPonting C.P.
TitleDomain homologues of dopamine beta-hydroxylase and ferric reductase: roles for iron metabolism in neurodegenerative disorders?
SourceHum. Mol. Genet. 10:1853-1858(2001).
PubMed ID11532994

3AuthorsBashtovyy D. Berczi A. Asard H. Pali T.
TitleStructure prediction for the di-heme cytochrome b561 protein family.
SourceProtoplasma 221:31-40(2003).
PubMed ID12768339

PROSITE is copyrighted by the SIB Swiss Institute of Bioinformatics and distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives (CC BY-NC-ND 4.0) License, see prosite_license.html.


View entry in original PROSITE document format
View entry in raw text format (no links)