Not available outside of the UK & Ireland.

Analysis Note

Heme content measured using difference spectroscopy. An extinction coefficient of 100 mM^-1 for the absorbance difference between 490 nm and 424 nm is used to calculate the concentration of cytochrome b₅.

Biochem/physiol Actions

Cytochrome b₅ is a membrane-bound heme-containing protein that enhances the catalytic efficiency of some P450 isoforms. Its mechanism of action is unknown.

Cytochrome b5 (CYB5A) mediates NADH-dependent reduction of methemoglobin (erythrocytes), electron transfer to fatty-acid desaturases (mainly liver) and steroid and xenobiotics metabolism by cytochrome P450 enzymes. It is essential for androstenedione synthesis. CYB5A helps in the efficient synthesis of gonadal androgen.

General description

Cytochrome b5 (CYB5A) gene codes for cytochrome b5 protein. It is located on human chromosome 18. It is co-expressed in the Leydig cells of the testis and theca cells of the ovary.

Physical form

Solution in 20 mM phosphate buffer, pH 7.25, with 0.1 mM EDTA