InterPro

Cytochromes b5 are ubiquitous electron transport proteins found in animals, plants and yeasts [PMID: 2752049]. The microsomal and mitochondrial variants are membrane-bound, while those from erythrocytes and other animal tissues are water-soluble [PMID: 4030743, PMID: 8439576].

The 3D structure of bovine cyt b5 is known, the fold belonging to the alpha+beta class, with 5 strands and 5 short helices forming a framework for supporting a central haem group [PMID: 1167544]. The cytochrome b5 domain is similar to that of a number of oxidoreductases, such as plant and fungal nitrate reductases, sulphite oxidase, yeast flavocytochrome b2 (L-lactate dehydrogenase) and plant cyt b5/acyl lipid desaturase fusion protein.

This conserved site includes the first of the two histidine heme ligands, which are found in the heme-binding domain of cytochrome b5 family.