Cytochrome b5 reductase is an enzyme in the blood. It controls the amount of iron in your red blood cells, and helps the cells carry plenty of oxygen.
Persons who do not have enough of this enzyme may develop a condition called methemoglobinemia.
Hoffman R, Benz Jr. EJ, Shattil SJ, et al., eds. Hematology: Basic Principles and Practice. 4th ed. Philladelphia, Pa: Churchill Livingston; 2005:655-656.
Goldman L, Ausiello D. Cecil Textbook of Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:1226-1228.