What is Cytochrome b5

Cytochromes b5 are ubiquitous electron transport hemoproteins found in animals, plants, fungi and purple phototrophic bacteria. The microsomal and mitochondrial variants are membrane-bound, while bacterial and those from erythrocytes and other animal tissues are water-soluble. Cytochromes b5 (cyt b5) are ubiquitous electron transport proteins found in animals, plants and fungi. A form of methemoglobinemia, a hematologic disease characterized by the presence of excessive amounts of methemoglobin in blood cells, resulting in decreased oxygen carrying capacity of the blood, cyanosis and hypoxia.
The family of cytochrome b5-like proteins includes (besides cytochrome b5 itself) hemoprotein domains covalently associated with other redox domains in flavocytochrome cytochrome b2 (L-lactate dehydrogenase; EC 1.1.2.3), sulfite oxidase (EC 1.8.3.1), plant and fungal nitrate reductases (EC 1.7.1.1, EC 1.7.1.2, EC 1.7.1.3), and plant and fungal cytochrome b5/acyl lipid desaturase fusion proteins. The enzyme from the control LCL (c 252/B 95) was found to be immunologically related to the human soluble erythrocyte cytochrome b5 reductase, indicating that it is the product of the same gene: the DIA1 (diaphorase) locus.
Cytochrome b5 is a membrane-bound member of the cytochrome b family. A heme protein that functions as an electron carrier for many membrane-bound oxygenases, cytochrome b5 possesses two heme groups, which are not covalently attached to the protein. The LCL derived from one patient with the type I disease and two patients with the type II disease were investigated.l In the former the defect was expressed to a lesser degree than in the cases with mental retardation in which the defect was much pronounced, and involved both the mitochondrial and the microsomal fraction.