Cytochrome b5-like Heme/Steroid binding domain
SMART accession number:SM01117
Description: This family includes heme binding domains from a diverse range of proteins. This family also includes proteins that bind to steroids. The family includes progesterone receptors such as O00264 ((PUBMED:9705155),(PUBMED:8774719)). Many members of this subfamily are membrane anchored by an N-terminal transmembrane alpha helix. This family also includes a domain in some chitin synthases. There is no known ligand for this domain in the chitin synthases.
Interpro abstract (IPR001199):

Cytochrome b5 is a membrane-bound hemoprotein which acts as an electron carrier for several membrane-bound oxygenases [ (PUBMED:2752049) ]. There are two homologous forms of b5, one found in microsomes and one found in the outer membrane of mitochondria. Two conserved histidine residues serve as axial ligands for the heme group. The structure of a number of oxidoreductases consists of the juxtaposition of a heme-binding domain homologous to that of b5 and either a flavodehydrogenase or a molybdopterin domain. These enzymes are:

  • Lactate dehydrogenase (EC [ (PUBMED:3004948) ], an enzyme that consists of a flavodehydrogenase domain and a heme-binding domain called cytochrome b2.
  • Nitrate reductase (EC 1.7.1.-), a key enzyme involved in the first step of nitrate assimilation in plants, fungi and bacteria [ (PUBMED:3393528) ]. Consists of a molybdopterin domain, a heme-binding domain called cytochrome b557, as well as a cytochrome reductase domain.
  • Sulfite oxidase (EC [ (PUBMED:510290) ], which catalyzes the terminal reaction in the oxidative degradation of sulfur-containing amino acids. Also consists of a molybdopterin domain and a heme-binding domain.
  • Yeast acyl-CoA desaturase 1 (EC; gene OLE1). This enzyme contains a C-terminal heme-binding domain.
  • Yeast Scs7 (YMR272c), a sphingolipid alpha-hydroxylase.

Proteins containing a cytochrome b5-like domain also include:

  • TU-36B, a Drosophila muscle protein of unknown function [ (PUBMED:2549511) ].
  • Fission yeast hypothetical protein SpAC1F12.10c (C1F12.10c).
  • Yeast Irc21 (YMR073c), a putative protein with unknown function.
Family alignment:
View or

There are 28640 Cyt-b5 domains in 27276 proteins in SMART's nrdb database.

Click on the following links for more information.