Cytochrome b5 isoform 1 （CYB5A） is a member of the cytochrome b5 family. CYB5A is a membrane bound hemoprotein which functions as an electron carrier for several membrane bound oxygenases. Defects in the CYB5A gene are the cause of methemoglobinemia CYB5A-related （METHB-CYB5A）， which is 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）.
