Cytochrome b(C-terminus)/b6/petD: Cytochrome b is a subunit of cytochrome bc1, an 11-subunit mitochondrial respiratory enzyme. Cytochrome b spans the mitochondrial membrane with 8 transmembrane helices (A-H) in eukaryotes. In plants and cyanobacteria, cytochrome b6 is analogous to eukaryote cytochrome b, containing two chains: helices A-D are encoded by the petB gene and helices E-H are encoded by the petD gene in these organisms. Cytochrome b/b6 contains two bound hemes and two ubiquinol/ubiquinone binding sites. The C-terminal domain is involved in forming the ubiquinol/ubiquinone binding sites, but not the heme binding sites. The N-terminal portion of cytochrome b, which contains both heme binding sites, is described in a separate CD.
Jiyao W et al.(2023). "The conserved domain database in 2023.",