Cytochrome b5 (CYB5)

Cytochrome b5 is a small, highly conserved hemoprotein and electron carrier, found in the membranes of the endoplasmic reticulum and outer mitochondrial membranes across a broad range of organisms including humans, animals, plants, fungi, and bacteria[1][2][3][5][7]. It contains a heme-binding domain and typically consists of 120–158 amino acids with a single transmembrane span anchoring it to membranes[2][7][8]. Cytochrome b5 functions as an electron donor in various oxidative reactions, notably supporting cytochrome P450 enzymes, contributing to fatty acid desaturation, steroid biosynthesis, lipid metabolism, and detoxification pathways[1][3][5][7][9]. It participates in both anabolic and catabolic cellular processes and is essential for normal metabolic function. Two forms exist in mammals: the microsomal (type A, CYB5A) and the mitochondrial (type B, CYB5B), displaying some structural differences but broadly similar roles[6][2]. Cytochrome b5 itself is not a primary therapeutic target, but its interactions with drug-metabolizing enzymes (notably cytochrome P450s) are vital for the bioactivation and clearance of drugs, making it an important accessory protein and sometimes implicated in metabolic and malignant diseases[1][3][5][9].

Other names

Microsomal cytochrome b5 type ACYB5ACYB5MCB5Cytochromes b5

Electron donor for cytochrome P450 enzymes, NADH-dependent or NADPH-dependent electron transfer