Cytochrome b5 is a membrane bound hemoprotein which function as an electron carrier for several membrane bound oxygenases. May play a key role in the modification by desaturation of fatty acids in the endoplasmic reticulum, which in the developing seed is utilized for membrane synthesis and in the developmentally regulated production of large amounts of storage lipids. Specifically expressed in developing seeds. Belongs to the cytochrome b5 family.