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 the normal amount of oxygen.
Persons who do not have enough of this enzyme may develop a condition called methemoglobinemia.
Bunn HF. Approach to the anemias. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed.Philadelphia, PA: Saunders Elsevier; 2011:chap 161.