Heme-binding protein which promotes neuronal but not astrocyte differentiation. Expressed in various tissues including brain, heart, adrenal gland, and kidney. In the brain, mainly expressed in pyramidal cells around the CA3 region of Ammon horn in hippocampus. Present in brain (at protein level). Abundantly expressed in the developing brain, in subventricular and ventricular zones of the cerebrum, where neural stem cells and neural precursor cells primarily exist. Expression levels gradually increase during brain development, between 14.5 dpc and P49. The cytochrome b5 heme-binding domain was proven to bind heme, although it lacks the conserved iron-binding His residues at position 73 and 106. Non-classical progesterone receptors involved in extranuclear signaling are classified in 2 groups: the class II progestin and adipoQ receptor (PAQR) family (also called mPRs) (PAQR5, PAQR6, PAQR7, PAQR8 and PAQR9) and the b5-like heme/steroid-binding protein family (also called MAPRs) (PGRMC1, PGRMC2, NENF and CYB5D2). Belongs to the cytochrome b5 family. MAPR subfamily. Probable cloning artifact. Probable cloning artifact. Probable cloning artifact.